You could add color to SECTIONS, but you can't colorize the entire clip with multiple colors.
One thing to do is to
Duplicate track
Drop chromakey on second track, key on a greyscale that's not too predominant
add color desired
child to first track.
Control opacity of color on second track to desired level.
I used a similar [overlay] technique to colorize a character's eyes in a test video. For that I exported frames, created rotoscoped overlays in Paint Shop Pro (PNG files), brought the rotoscoped frames back into VV3 and tweaked the opacity and blur. A bit of work, but did the trick.
a really cool way is to use the gradient map filter. it is one of the new filters in the add-on filter pack available from SF. you can customize a whole gradient of unlimited colors, the hues of which will be chosen based on the luminosity of your source pixels.