Obviously, the jumpsuit idea came from the second issue of the Mirage comics, but the yellow jumpsuit and white boots were probably a product of either Playmates or Fred Wolf Films input.
I'm really surprised nobody has drawn attention to the similarities between Old Toon April and Mel Bush from the 1986-1987 seasons of
Doctor Who.
I know David Wise has been a huge Doctor Who fan over the years, so it wouldn't surprise me if he somehow influenced the design process for the pilot episodes. I guess somebody could probably ask him on his Facebook page or something.