You obviously mean in the summer. How about the old standby trailing blue lobelia, the darkest royal blue.

What about Bacopa? That's another good trailing plant. You can get it in white or pale lavender. It flowers and flowers, too. There are also foliage plants that would go alongside the flowering ones, like Dichondra. The silver-leaved one would look great with Lobelia or Bacopa and the Gazanias.

Good luck and happy planting.

what about diacias too.

I have zinnia profusion among mine.