The entrance and descent of the Atman into the phenomenal world via man is through Brahmarandra and the Sushumna tunnel of Maha Kundalini Sakti the major nadi that ends in the Kundalini chamber. In time like the lotus the seed grows through the so to speak - impure land then impure and pure land then finally into the pure land and fulfilment. Man when fully matured and purified is also said to have opened a thousand petal lotus on his head, the sahasrara chakra as displayed on the iconography of Buddha - the awakened one. From Brahmarandhra a jewel is born. Do Hindu scriptures varify this jewel and if so what is its color and its atributes?
Some of your questions are like - Is this concept myth or real?
Now, in answers we should simply say whether the concept is found in Hindu scriptures or not. If it is not then it's a myth and if it is then it is real. I don't know of other ways of answering such questions.
Brahmarandhra, Sushumna Nadi have been mentioned in many many Hindu scriptures including the Tantras, Upanishads etc. So, they are all real.
From Hatha Yoga Pradipika (HYP) for example:
Sushumnā śūnyapadavī brahmarandhrah mahāpathah
Śmaśānam śāmbhavī madhyamārghaśchetyekavāchakāh ||
Susumnâ, Sunya Padavî, Brahma Randhra, mahâ Patha, Śmaśâna, Śambhavî, madhya mârga, are names of one and the same thing. (HYP 3.4)
For the Yogis there are 16 vital places (one among which is the Brahmarandhra) as given in the following verses:
अगॊ षु गलु जानरू सीवनीशरङनाबम् ।
हदीवा कणिदशे ि रशमका नाशसका तथा ॥
भभू धॊ च रराटॊ च भधू ात च बहयनकभ ।
एते शह षोिशाधाया् कशथता् मोशगऩङु व्ै ॥
The sixteen vital parts mentioned by renowned Yogîs are the (1) thumbs, (2) ankles, (3) knees, (4) thighs, (5) the prepuce, (6) organs of generation, (7) the navel, (8) the heart, (9) the neck, (10) the throat, (11) the palate, (12) the nose, (13) the middle of the eyebrows, (14) the forehead, (15) the head and (16) the Brahma randhra.
Of all the Nadis, the Sushumna is the only one useful for the Yogis, as it ends in the Brahmarandhra. The God entering the bodies through that pore is also mentioned in Upanishads.
So, such concepts are real.
But I haven't understood what you meant by the color of the jewel and crown. Do you mean to ask whether there is a real crown and a jewel in it in our heads?