No promises, but I might get back into this when Forza Horizon 5 comes out. If/when I get back into this, I will not be honoring requests. At this point, the vast majority of colors are in the spreadsheet. Any that aren't will probably be there eventually. As you said, people can and need to learn how to do this themselves. That's actually how I got into this; in about 2017 or so, I discovered
@Terronium-12's version of this project. While there were a lot of colors (for the time) available on that spreadsheet, there were a lot that weren't there, colors that I wanted to use. I posted requests in the Forza 6 and Horizon 3 editions of this thread, but to no avail. So, I decided to learn how to do this myself. At first, my recreations weren't 100% accurate, but they got better to the point where I'm at now.