If you've ever worn racerback tops, much like this Express Sexy Basics Racerback Tank ($17), then you know that they have a slight flaw. If they're cut too low, your bra ends up showing from the sides and back. Unless you want to pull a Carrie Bradshaw, I came up with a solution without sacrificing comfort.
To see how I solved this racerback issue,
Bandeau bras, like this Damsel Seamless Bandeau ($8, originally $12), are fun but they provide no support, especially for bustier gals. So my advice is to wear your regular strapless bra underneath your racerback top, but then cover it up with a colorful bandeau bra. That way, the bandeau shows and not your bra. It's a win-win: you get support and pizazz. I suggest picking a contrasting color from your top for a funky feel.