I am SOOOO jealous that your stash is organized by colors! That would be so amazing! I can't tell you how many times I just wanted to search by colors rather than a theme! I usually just go to my BYOC folders then and look at the previews until something catches my eye, but your system would be so much faster!
When I started digi 20 years ago I created a system that sorts by store, then designer. I also keep BYOC, DYD and those types of collections together since they are the same colors and were made to coordinate.
At first I could usually remember everything in my stash and knew where to find things... but now there just so much and I can't always think of a kit based on them, so several years ago I started a "Themed" folder too. Inside that folder I have sub-folders for a bunch of themes I use over and over again. In each folder I copy the preview of a kit that would work for that theme and then I create a link in that folder that will take me to the kits location. That was the best way I could sort of replicate tags without having to go back and tags my whole insanely large stash.