Colours may also be indicated using English words:
red, orange, yellow, green, blue, violet, black, gray, silver, white, brown, aqua, fuchsia, lime, maroon, navy, olive, purple, teal.

But it is also possible to create colour shades yourself, by specifying the preferred mixture of red, green and blue. Each colour for the blend consist of two hexadecimal digits, between 00 and ff, three pairs with a number sign in front. So #000000 is black, #ffffff is black (you may just as well write #FFFFFF), #ff0000 is red, etc.

See also this Color tester.