We know that the complexion of Lord Vishnu / Krishna is dark (shyam varna) but what is the complexion of Lord Shiva, dark or white?
Lord Shiva's Complexion was described in Chapter Four (Cancula's Salvation) of Shiva Purana Mahatyam in Shiva Puranam. You can see that from here.(Page 18)
She saw the three-eyed Mahadeva, the eternal, being served devotedly by Brahma,Vishnu and other gods.
He had the brilliance of ten million suns and was reverently served by Ganesha, Bhrngi, Nandisa, Virabhadreshwara and others.
His neck had a blue hue ; he had five faces, three eyes , the cresent moon as crest-ornament and his left hand was apportioned to Gauri , who had the brilliance of lighting.
He was white in complexion like camphor and wore all ornaments. Besmeared with white ashes all over the body and clad in white clothes,he shone brilliantly.
The woman Cancula became highly delighted on seeing Shankara.In her flutter of delight she bowed again and again to Him.
The complexion of Shiva is white. He is described as Karpura Gauram- white like camphor. But, the complexion of Maha-Kala and Kala Bhairava is Black, as they represent time and annihilation.
This may be of interest to you- http://pratyasha.deviantart.com/journal/Shiva-is-not-Blue-but-White-371562557
One of the common "śloka" chanted right after "Aarti" and It is found in Yajurveda, one of the four canonical texts of Hinduism is below one, in Praise of Lord Shiva
कर्पूर गौरम करूणावतारम संसार सारम भुजगेन्द्र हारम | सदा वसंतम हृदयारविंदे भवम भवानी सहितं नमामि ||
The first word in above sloka, describe the complexion of Lord Shiva.
कर्पूरगौरं (karpūragauraṁ): The one who is as pure/white as a camphor(karpur)
we are human being and always like to see god in same form as human being. shankar portrait as human being but shiva is in form of shiv liga, which represent universe or shape of universe or shape of energy, and major part of universe is emptiness. and this emptiness is black in color.
worship of shiva is worship of emptiness or align with universe or harmonize with existence.