Awesome job. I know what you mean about the plasti becoming white.
I tried this same thing on a dingy and yellowed 1/55 GBP-1S using a over the counter 3% solution, but it took 4 months to actually see results. I kept the parts in the sun for a week and nothing happened. Then, at the second week up until the 4th month, I left the parts in my garage. I did remove all the yellow but turned he blue parts light blue, while the red and white cleaned up really nicely and held their color.
The reason why I left the parts soak for 4-months is that I totally forgot about them. But hey, it still works.
Just a note: remove all metal parts as they will oxidize due to the hydorgen peroxide.