"Shades" in this sense refers to the varieties of a single colour (a series of colours in this case). This is the most plain and direct word for this meaning. Nuance may be used in reference to colours, but tends to mean more subtle differences than shade. However, nuance is more often heard metaphorically, referring to subtleties of idea, concept, speech, etc. (Shades may also be used metaphorically, of course, as in "shades of meaning".)
I think you should use a thesaurus for synonyms rather than asking here; however, one word that springs to mind is "hue".
Thanks, my dear friends, for your help and the advice.
As a minor aside, it's not that I'm too lazy to consult a dictionary or a thesaurus but that I'd like to hear what living and kicking native speakers say about it in person. In this way, I can learn better in a meaningful way.