Try coloured top mats- suede mattes are particularly rich in colour. I use suede mattes all the time for my personal collection. Try zany frames. Frames can be multi-coloured, or beautifully textured with leaf carvings, daisy patterns, etc. Usually a simple shape like a diamond is best.
Panelling is another option.
The framer cuts a very thin area into the top mat to reveal the colour underneath. Usually in a rectangular pattern. Try a fillet. Fillets are frame-type materials that are very thin, and are used to surround the visual area of the piece right next to the mat. Matching the fillet to the larger frame can be quite stunning.