Avoid having users select a color from a dropdown with color labels (‘red’, ‘black’, etc.). Make them choose the color variant from a list of color swatches (circles or squares filled with color) or small thumbnails of the product in different colors.

If some of your products have multi-color design variants and some are a single color, then you can use both (color swatches and thumbnails), depending on the type of variants.

See Sears below as an example of that mixed approach.