I think the time and frustration involved would warrant a price so high that customers would not buy them.
I have injected 3 colors and will only do it for personal use because it is a pain and takes forever.
Customers buy 3 colors all the time in large quantities. Prime example is sexy shad or foxy shad.

On average, 3 color really does not take much more time. I don't charge anything more for a 3 color bait vs a 2 or single color bait.
4 colors might be overboard but also may catch on, depends on the resulting bait and IF it catches fish!
Jim