Unlike most Sith who ware black, upon his baptism he wore completely white armor to contain his essence. However, through the visor one can see his true colors.
He embraced the Dark Side in a very unique way: Instead of anger or hate, his primary source is his passion and pride. He desires purely to now twist the Force as a pure tool of corruption and darkness. He became balanced, both emotion and logic, the defined "light" and "dark" sides equal.
But the true essence of the Dark Side; twisting the very fabric of the laws of the universe, is now his full being. The true Light Side, having the natural order and will of the Force guiding him into a natural balance, is far from him.
As such he has wrapped himself in what little light remained of his former body, disguising his true nature.
He was born a boy, a very lovable young lad who desired simply to go out and see the universe. But when a Sith Lord came and tempted him with both his desire for exploration and with offering him power he gave in, killing his brother as initiation. At that time there was still some good in him, and he was also the definition of the formal detailed "Dark Side"; filled with anger and hate.
It was the Gungan jedi padawan, Toe Toe Kaital, who inspired him to become the ultimate evil. Toe Toe's attempts to convince him of the true nature of the Light Side gave him a glimpse into the true division of Light and Darkness.
Then, when Toe Toe Kaital refused to kill Lucium after dismembering the sith warrior, he contemplated his life. When he realized what he wanted to become he slid himself over to the lava, after the Jedi had left, and immersed himself; forcing his will to overcome the lava. It worked, the energy in the lava, through the pain of the immersion, was twisted into dark side energy. Lucium's body itself was all but destroyed, it's charred remnants only held together by the darkness itself.