If you want to invest the time and money it can be done.
That line is Very Important. One needs to insure they either do it (or have it done) Right, or Don't do it at all. Be certain the process used not only re-colors, but also re-hardens, the parts. If not live with what colors you have, or don't have, the original hard case was not lost, only the colors.
There are several outfits who have done much research into this & can do a good job.
I am a great one for Doing it Myself, but this is not a job for a DIY'er unless you are willing to do a lot of investigating & a considerable outlay of cash for the start-up. From a previous thread on this subject a few weeks back it appears that B'999 has done his study well & had some good help. You would likely do well to listen to what he has to say on the subject.