Answer:
I usually wear a yellow coat. I usually have a dark head. I make marks wherever I go.
At first, I am nothing. Add something to negate. Add again to oppose. Add again to find the time to draw. Add once more to find nobody at all.
My first is nothing but a name; my second is more small; my whole is of so little fame it has no name at all.
A precious stone, as clear as diamond. Seek it out whilst the sun's near the horizon. Though you can walk on water with its power, Try to keep it, and it'll vanish within an hour.
Searing 'cross the pitch-black skies, I scream in celebration, Yet moments later, my outburst through, I am naught but imagination.
What sphinxes employ and players enjoy.