I gave it my best shot.
I sanded it down and did the stitching, which I'm not good at, then painted the entire white part black, then sprayed on white and applied a gradient paint. I roughly applied pearl white and painted the whole thing while separating the colors. I applied a matte and glossy top coat for now.
The shell unit was printed and finished in rainbow colors with a highlighter pen. I tried to make it glow under black light. I also added fluorescent paint to the stitching marks, but after applying the top coat it didn't glow as much. I think it turned out better than the plain version.

HG Gundam Caliburn - Fully painted realistic finish | ココソウ's Gunpla works