In a previous motorhome we replaced all the carpet with Allure, but couldn't figure out how to to the hump or dog house in the class A mh. So we used rit dye to dye it. I mixed the die in a pistil grip sprayer, put on a glove, sprayed it and worked it in. It looked great, but I did notice some fading after a while...just spritzed it again.
Here is a link to my blog post about the dye job and some pictures of before and after.
Remember though, we only did a small area. It would take a while to do all the carpeting and my method would be very slow. It would probably be a wonderful improvement though.