That’s an interesting and original approach. I like it! In the end, the right solution for color could indeed be a mix between your RGB light system and simple collimation by condensers like on our good old Durst enlargers. Your tests are going to be fascinating!
For my part, I’m starting to think about how to improve my prototype. And I’ve found these lenses that might be interesting?
https://www.edmundoptics.fr/p/100mm-dia-x-150mm-focal-length-pcx-condenser-lens/35971/