Michele's advice is on the money, Carolyn. Some shows will not accept colored mats at all.
You must also check with them before framing as many shows require Plexiglas instead of regular glass.
One of the things you might consider in choosing a frame is selecting one that would be a good frame for all your work under glass, and one that is affordable enough to frame enough peices for a show or exhibit of your own.
Some years ago I decided to use a standard mat and frame for all my pastels (mine are very inexpensive, I get them from Frame Fit here:
http://framefit.com/) as I can deliver a framed piece to clients, offer to buy back frames if they would (PLEASE!) go to a professional framer, and they don't cost enough for me to worry about ever seeing again. I began working in standard sizes some years ago, so I can order a bunch of frame pieces at a time, and always have the right size on hand. The plus is that when I would do an exhibit,I would have uniform frames...improving the look of all my work as a cohesive body, rather than it looking like I spent most of my time framing at garage sales.
When I started to do oils some years later, I bought a number of handmade frames, also in the common standard sizes I tend to use, that are actually beautiful (and $). When I exhibit oils, they too have a cohesive look. If someone wants to buy one of the frames I have, that's fine, but I have no interest in becoming a framer. I can just pop paintings in and out of various frames, whatever I might need for a given show or presentation. Although my frames are expensive, they look it, and show my work off to its best.
Good luck!