I love gray as a fashion color but haven't worked with it a lot. I do go in trends of what colors I want to work with. Couple of years ago I did a lot in browns, I have declared this year the year of the brights. Maybe next year my eyes will need a rest from the brights. Hard to say at this point.
Back in the 30s, green and yellow was the neutral combination. I tend to use a focus fabric (which can end up as the back) and choose the colors from there whether it is primary or pastel or theme.
Snooze, for me it was Scrap Quilts by Judy Martin. The directions are out of style now, templates even! But the pictures and discussion are still valuable.
https://www.amazon.com/Scrap-Quilts-.../dp/096029709X
Before that I always did what I now call "planned quilts" and I had never seen a scrap quilt I considered attractive. Maybe because I don't have a family background of quilts.
Now, I work almost exclusively in scraps or what I'm currently thinking of as collections.