"Color variants" refers to different versions or options of a particular color. It can represent shades, tones, or hues that slightly differ from the original color. Full definition
In this short video, the designer showed off a number of color variants of the device, including the all - red model, the black + red model, and so on. (androidheadlines.com)
I got the gold color variant for the review. (gogi.in)
Only the Black color variant of the device is available as of now. (gadgetian.com)