When it comes to dressing baby you're pretty much at the mercy of the clothes manufacturers. Everything is either sold in sets or meant to be a set. It's almost impossible to find solid onesies in specific colors or solid bloomers sold separately.
I was just browsing the internet and for some reason thought of American Apparel. Although their selection isn't great they sell solid separates for a pretty good price. I feel like I'm always looking for a solid undershirt for a cute sweater or solid leggings to go with a dress. Now I have a place to look.