You will need to create a mask around the body to let the color version show through. If the player is moving, the mask will have to follow the player. Bezier Masking can do this but will be very time-consuming.
I replied to Coursedesign in regards to Combustion, and anyone else who might be interested in what I have found from using all the apps out there. Combustion is also very good, but I prefer Fusion, just like I prefer Vegas over FCP (which is also very good).The original poster can probably use Vegas for roto as suggested earlier on.
This is simple to do in Vegas if you are only changing one color. If you have more than one color, you need software with motion tracking as the folks above state.
The other issue is the one color you are changing will be adjusted for all shades of that color. You can narrow this down, by adjusting the settings. but if you are adjusting, blue all blues may be affected. In a sports situation. every player on that team will be wearing a similar color and most likely ALL the jerseys will change color.