I get "stuck" when a fabric can go nicely into more than one category -
Examples:
Black and white cat print - does it go with the cat fabrics? does it go with the black and whites?
Large multi-colored floral on black background -
Small/tiny florals - by color or style?
The colors that are sort of "in-between" - The bluish green that isn't quite aqua or teal - the blue that is sort of purplish, but not quite purple