Do you know the saddle brand? If so you can look for matching leathers. Some brands' idea of a color is different than others. Also, it depends on what kind of stirrups you want to buy. You can get regular cheap ones like in the ad that kitten posted or spend more and get safety irons or stirrups that improve position and act as shock absorbers. If you go to sites like statelinetack.com & doversaddlery.com you'll see a wide selection of what you're looking for.
Most adults or full grown teens take 54" leathers. If you're short, 5'5" or under, you would do likely best in 48" leathers.
4 3/4" stirrup irons are standard adult size. If you have really small feet, size 6 or smaller, then 4.5" irons would probably be better. I prefer peacock or similar safety irons for jumping. If you're a Dressage rider, jointed irons are great. If you do both jumping and dressage, then stick with the safety irons.