What about modelAs?
seems to be a masculine only word, but can change the article to las to indicate female
and the "peek" when you mouse over the word model has modela as one of the translations
why is it not negras because male models don't wear dresses, right?
It's because dresses are masculine. Whether the models are male or female doesn't matter.
colors are also supposed to match in terms of pluralization? e.g. negro vs negros
yep! There might be some colours that don't follow this rule, but I can't think of any so I might be thinking about french... But regardless, yes, you have to make your adjectives agree numerically with your noun as well as by gender. :)