Monster ideas for a "color" themed game?

[Etinarg]

There's always self-replicating Grey Goo.

The technology level in my project isn't that advanced, but multiplying, acidic grey slimes, jellies or grey oozes surely are an option.

[NatalyAnders]

colour-related lists: not quite what you're asking, but in that direction:

http://www.macmillandictionary.com/thesaurus-category/american/General-words-used-to-describe-colors
http://phrontistery.info/colours.html

The first one looks like it has more fun stuff.

And one more definitions http://www.dictionary.net/color.

[NatalyAnders]

colour-related lists: not quite what you're asking, but in that direction:

http://www.macmillandictionary.com/thesaurus-category/american/General-words-used-to-describe-colors
http://phrontistery.info/colours.html

The first one looks like it has more fun stuff.

One more definition http://www.dictionary.net/color

[Hi]

one of them can be named Darren