You would do well to look for "black" flowers, since they are really dark purple or deep red. A couple that I've considered (but haven't tried) are scabiosa "ace of spades" and cornflower "blackball". A dark coleus might work for you.. the "palisandra" or "black dragon".

I'm growing snapdragon "black prince" right now - the foliage is twinged with maroon and the flowers are expected to be a deep red. I hope to pair it with zinnia "envy". Should be a neat combination.. good luck!

What about japanese eggplant, golden japanese sedum "Ogon"and purple oxalis?! :-)

I made some beautiful containers with deep purple Petunias and the chartreuse Sweet Potato Vine and 'Blackie' Sweet Potato Vine. They made a great combo.

I had a window box a couple of years ago planted with the chartreuse potato vine and the extremely dark burgundy geraniums among other things but found this very dramatic.

Japanese blood grass would add a nice blend between the chartreuse and deep purple.

I just made one this weekend with purple heart, chartreuse sweet potato vine and pink wave petunias. Its already gorgeous!

I saw a beautiful hanging basket the other day, it was homestead purple verbenum and a varigated yellow lantana. I WANTED that basket LOL