I'm curious, how old is she? She's a bit on the thin side, so you'll want to put some meat on her little bones before putting her in the show ring. She'll need her bridle path clipped. I'm not sure how far they do them. I know for a quarter horse it's the lenght of the ear, I think maybe a couple inches past that for an arab? You'll want to shave her little nose...
As for colors, are you showing english or western? If you are showing english then you will wear the regular colors, beige or grey pants and a blue, grey, or green jacket, although I don't see green around much anymore... You can do the square english pad in any color. White would be pretty classy, but with your mares coloring you could do anything, pink would even be cute.
"Be a best friend, tell the truth, and overuse I love you
Go to work, do your best, don't outsmart your common sense
Never let your prayin knees get lazy
And love like crazy"