I know there are multiple rudras, the rudra born from brahma is said to be red and blue in colour, but sankar or ShiVa are said to be karpur gauram and nila kantham, what's the difference between the two?
There are infinite Rudras. In the 11th Anuvaka of Sri Rudram too we find:
नमो रुद्रेभ्यो ये पृथिव्यां येऽन्तरिक्षे ये दिवि येषामन्नं वातो वर्षमिषवस्तेभ्यो दश प्राचीर्दश दक्षिणा दश प्रतीचीर्दशोदीचीर्दशोर्ध्वास्तेभ्यो नमस्तेनो मृडयन्तु ते यं द्विष्मो यश्च नो द्वेष्टि तं वो जम्भे दधामि ॥
We render obescience to those myriad manifestations of Rudra whose weapons are food, air and rain; who exists in earth sky and heaven. Prostrations to the east, to the south, to the east and to the north and upwards. Let them render us happy, whoever hates us and whosoever we hate consign in your wide open mouth.
So, it's possible that there are many Karpura Gauram Rudras and many NilaLohita Rudras. We may not find their stories in scriptures also.
But at least we know from Purana that Karpura Gaura Rudra is SadaShiva who first manifested from Sat-Asat state. As described in answer here:
When there is a pitch darkness that cannot be pierced with needle and what is mentioned in Vedas " The Existent and that Brahman" is alone present. When the present visible world is not in existence, the Sat Brahman alone is present which Yogins observe perpetually in the inner Soul, the inner firmament. It is incomprehensible to the mind. It cannot at all be expressed by words. It has neither name nor color. It is neither thick nor thin. It is free from alternatives. It has no beginning nor end. It is free from illusion and its harassment. It has no second. It has no development. It is in the form of Pure knowledge. People have doubts giving it a name. That Being after, then after sometime, it is said, wished for a second. The Being, having no form of its own, wished to create, in the course of its own sport, an auspicious form its own endowed with all power, qualities and knowledge. A form of that goes everywhere, that has all forms, that sees all, that is the cause of all, that should be respected by all, that is the beginning of all, that bestows everything, and that sanctifies everything should be created (So it is wished) and hence created that form of ISVARA of pure nature. The Original Being without a second, with neither beginning nor end, that illuminates everything, that is the form of cit(Pure Knowledge), that which is termed as Supreme Brahman, the all-pervasive, and undecaying, vanished. The manifest of formless being is SADAASIVA. Scholars of ancient and succeeding ages have sung is ISVARA. ISVARA though alone ,then created the physical form Saktiform his body. This Shakti did not affect his body in any way. This Shakti is called by various names. Pradhaana, Prakriti, Maayaa, Gunavati, Paraa. The mother of Buddhitattva (The Cosmic Intelligence), Vikritivarjita (without modification).That Shakti is Ambika,Parkriti and goddess of all. She is the prime cause and mother of three deities. She has a brilliance which could hardly be conceived. She is the generating cause of all. She sprang up singly as Maaya. In her union she manifested into various forms. The Supreme Purusha is Shiva. He is called Shambu. He has no other lord over Him. He has five faces. He has ten arms. He holds the trident. He is as pure and white as camphor. His body is dusted entirely with ash. Shiva thought within Himself like this-" Another being shall be created by me. Let him create everything, protect it and in the end dissolve it. The supreme lord , Shiva , spread liquorice essence of nectar on His left side, on tenth limb, nectar which was the outcome of churning the ocean of His mind wherein thoughts were the waves, Satva Guna was the precious Gem, Rajas being coral and Tama being crocodile. Thereupon a person came into being who was most charming one in the three worlds, who was calm with sattva guna prominent, and appeared to be ocean of immeasurable majesty.
And NilaLohita is that form who came out of Lord Brahma. I discuss it in my answer here:
ललाटमस्य निर्भिद्य प्रादुरासीत्पितामहात् ।
लोहितोऽभूत्स्वयं नीलः शिवस्य हृदयोद्भव ।।
वह्रश्चैव तु संयोगात्प्रकृत्या पुरुषः प्रभुः ।
नीलश्च लोहितश्चैव यतः कालाकृतिः पुमान् ।।
नीललोहित ईत्युक्तस्तेन देवेन वै प्रभुः । (Linga Purana 1.41)
All pervading lord born of body of Bhava, came out of Brahma by piercing his forehead. The lord who born of the heart of Shiva was originally blue but became red coming in contact with fire. It represents the form of combination of Prakriti and Purusha of the Lord. Because of the form with both blue and red colour resembling Kãla, Lord came to be known by the name NilaLohita.
There are a lot of rudras let me explain there is lord shiva he by partial incration became lord rudra to help bramha the 11 rudras are too for brsmhas help apart when bramha asked rudra to create beings he created immortals where there were need of mortals so they become rudras that's why in shatpath brahmana one place they are 11 and other place 33 In mahabharata they are 11000 rudras.
so,lets get start lord rudra and lord shiva both are called nila-lohita and nila-kantha which is discussed by tezz here and nilakantha is too lord shiva in my answer here Your answer can get support from here
Let's take a look at this shatpath bramana's other chapter :—
9:1:1:11. He then performs theSatarudriya offering! This whole Agni has now been completed: he now is the deity Rudra. Upon him the gods bestowed that highest form, immortality. Flaming he there stood longing for food. The gods were afraid of him lest he should hurt them.
9:1:1:22. They spake, 'Let us gather together food for him: therewith we will appease him!' They gathered for him that food, theSântadevatya, and thereby appeased him; and inasmuch as they thereby appeased (sam) the god (deva), it is calledSântadevatya;-- Sântadevatya, doubtless, is here called mystically 'Satarudriya,' for the gods love the mystic.
Anushasana parva of mahabharata:—
Thou art he that hadst created from thy right side the Grandsire Brahma, the Creator of all things. Thou art he that hadst created from thy left side Vishnu for protecting the Creation. Thou art that puissant Lord who didst create Rudra when the end of the Yuga came and when the Creation was once more to be dissolved. That Rudra, who sprang from thee destroyed the Creation with all its mobile and immobile beings, assuming the form of Kala of great energy, of the cloud Samvartaka (charged with water which myriads of oceans are not capacious enough to bear), and of the all consuming fire. Verily, when the period comes for the dissolution of the universe, that Rudra stands, ready to swallow up the universe. Thou art that Mahadeva, who is the original Creator of the universe with all its mobile and immobile entities.
— The Mahabharata, Book 13: Anusasana Parva: Anusasanika Parva: Section XIV
The shwetaswatra upnishad is one of the mukhya upnishads. The shwetaswatra upnishad 4.18
IV-18: When ignorance is dispelled, there is neither day nor night, neither being nor non-being. There is only shiva who is imperishable, and who is worthy of being adored by the creator. From Him has proceeded the ancient wisdom.
2Rudra is truly one; for the knowers of Brahman do not admit the existence of a second, He alone rules all the worlds by His powers. He dwells as the inner Self of every living being. After having created all the worlds, He, their Protector, takes them back into Himself at the end of time.
When Pragâpati had become disjointed, the deities departed from him. Only one god did not leave him, to wit, Manyu (wrath): extended he remained within. He (Pragâpati) cried, and the tears of him that fell down settled on Manyu. He becamethe hundred- headed, thousand-eyed, hundred- quivered Rudra. Andthe other drops that fell down, spread over these worlds in countless numbers, by thousands; and inasmuch as they originated from crying (rud), they were called Rudras (roarers). That hundred-headed, thousand- eyed, hundred-quivered Rudra, with his bow strung, and his arrow fitted to the string, was inspiring fear, being in quest of food. The gods were afraidof him.
9:1:1:77. They spake unto Pragâpati'We are afraid of this one, lest he should hurt us!' He spake, 'Gather food for him, and appease him therewith!' They gathered for him that food, theSatarudriya (offering), and thereby appeased him; and inasmuch as they thereby appeased (sam) the hundred- headed (satasîrsha) Rudra, it is called Satasîrsharudrasamanîya,-- and satasîrsharudrasamanîya, doubtless, is what they mystically call Satarudriya
from the verse of bhagwat geeta :-
I am Marichi among the Maruts, and the Moon among constellations. I am the Sama Veda among the Vedas; I am Vasava among the gods; I am the mind among the senses; I am the intellect in (living) beings. I am Sankara among the Rudras.
—— The Mahabharata, Book 6: Bhishma Parva: Bhagavat-Gita Parva: Section XXXIV (Bhagavad Gita Chapter X)
It says that among eleven rudras krishna is shankar as there are eleven rudras and all have different name mahabharat gives an account of two types of eleven rudras one from harvamsa parva and one from mahabharat. Before it was kapalin who was best among rudras now according to bhagwat geeta he is shankar who is best among rudras thats why krishna says among rudras i am shankar.
For proof click here :- https://en.m.wikipedia.org/wiki/Rudras clicking here you can knoledge abou rudras.
Some would be thinking how there are these much rudras ok some time it is called kalpa-bheda (diffences because kalpa of which it is mentioned.)
Ok here is the proof that will clear it:-
Eleven hundred Rudras stood around that Deity of restrained soul and white deeds, then seated upon his bull. All of them were employed in hymning his praises. The Adityas, the Vasus, the Sadhyas, the Viswedevas, and the twin Aswins praised that Lord of the universe by uttering the hymns occurring in the scriptures.
—— The Mahabharata, Book 13: Anusasana Parva: Anusasanika Parva: Section XIV
So here eleven hundred rudras are mentioned.
Likewise the Maruts are the foremost of the Ganas. Surya is the lord of all the planets, and Chandramas of all the constellations. Yama is the lord of the Pitris; Ocean is the lord of all rivers. Varuna is the king of the waters. Indra is said to be the king of the Maruts. Arka is the king of all hot bodies, and Indra of all luminous bodies. Agni is the eternal lord of the elements, and Vrihaspati of the Brahmanas. Soma is the lord of (deciduous) herbs, and Vishnu is the foremost of all that are endued with might. Tashtri is the king of Rudras , and Siva of all creatures.
—— The Mahabharata, Book 14: Aswamedha Parva: Anugita Parva: Section XLIII
And here we can see that Tashtri is the king of rudras and shiva lord of all creatures.