I was thinking of painting a frame with matte color but how Do I do to make the paint matte ?? is it special paint or is it a technique ?

Matte is an additive to paint. If you are "rattle can" painting, you can get flat black and possibly other flat colors as well. If you are using a compressor/gun/auto paint, then you add flattening agent to the final clear coat(s). As a note (from my personal experience) if you add too much flattening agent, then the clear becomes like fog and will add a white tint to your color. BIG BUMMER! Repainting will be needed to fix that glitch.
Hope that helps,
Dr. D mb at mbent dot net if you have more Q's.

rattlecan primers usually have matte finishes. I've seen olive green, white, and grey. from a paint standpoint I don't know how well they protect. the first frame I built I painted with a white etching primer, no top-coat. initially it chipped a bit but after a few years of curing it's on there for good. I usually buy my rattlecans at pep-boys.