The color value is unrecognized (e.g., 'multicolor', 'various', 'N/A'); use a real color name.
Each product attribute in Google's spec has format and value rules. Issues here are usually: missing required attributes for the category, invalid enum values (e.g., 'XL' submitted where 'M, L, XL' is the valid set), out-of-range numbers, or attributes that conflict across the feed.