Synonyms for Colorize:

n.

colorize (noun)
colorise, colourise, Colour In, colourize, colour, color, color in.

v.

variegate (verb)
dapple, check, checker, color, fleck, marble, stripe, striate, tessellate, freckle, streak.

Other synonyms:

colour in
Colour In.
Other relevant words:
colour, color in, colourise, colourize, Colour In, colorise.