You know, those gorgeous colorful, bright batiks are going to look a whole lot more colorful and bright with a bit of dark in there.
There is also a really, really dark navy/indigo-ish which is fabulous for making the lighter colors sparkle.
It's all about contrast and value.
I buy the really dark batik darks whenever I can find them in 3-5 yard lengths. I'm always finding a use for them.