I've figured out why Midge is wearing a blue polka dot sundress in the Life in the Dreamhouse episodes. Not only did she and Barbie wear blue outfits with white polka dots in 1988, when Midge was re-introduced in the California doll line, but it's probably also because there were a number of outfits in the 60s and 70s with that look. Remember these outfits? This cotton fabric appeared a LOT!
Barbie: Little Red Riding Hood, Cool N Casual, Fashion Bouquet
Skipper: Nighty Nice
Tutti: Ship Shape
Buffy: her Mrs. Beasley doll
Mattel must have bought thousands of yards of that fabric and had to keep using it!