All of the black pegasus (not just the mothers) have the rainbow colored wings. Here’s the link to the Windstone Store page with the Pegasus Family. I wish the black pegasus only had the blue to purple like the old black male griffin. I like that coloration better than the gold->magenta->blue->purple of the black pegasus family members. The black pegasi are limited production items.
The only other color the pegasi have come in is the white. The only pegasus that is still in current production (other than the limited blacks) is the hatching pegasus. The others (male, baby, mother) retired in 2004.