I feel your pain, it happened to me 2-3 times, between 2 and 4 hours of "work" lost! 😭
Each time I told myself "now you know, next time you won't forget to save every now and then", but I do forget sometimes anyway!
About the colour things, I didn't remember we could "bring" colours from one livery to another. I guess you mean the pallet kept the last colours we used on another one and not on THIS livery like in GT7.
When I need to keep several colours I screen the colours' details.
That's not perfect but at least I'm sure to have the exact same thing, and even if that means to find the previous car, open the livery editor, open the decal/paint details, yeah, that's faster than trying to figure out how to get that colour again! 😅