I've done a lot of scrappy quilts, and learned to keep a good differentiation between colors. I did one that was white/red/pink and ended up with some problems with pinks that were too red, and reds that were too pink and it messed up the pattern. I fixed some, but in the end really wished I'd pulled more of the red/white pattern fabric that was not at least 75% red - that messed up the pattern too.
You also have to be real careful with prints and as you are cutting, if the piece ends up looking like a different color because of how it's cut, don't use it. I did a quilt using Tiole, and had a lot of small triangles. As I was sewing I realized I has some that were nothing but the upper back end of the horse. I pulled about 6 of them out of the pile. I also pulled out any that had an area of intense printing, as they ended up reading way too black in a spot they were suppose to read mostly white.
I've been ignoring my fabric for this mystery. I've been so tempted to buy more and had to keep telling myself that I already have way more yardage than I'll need, and I have enough variety. I'm really bad at overbuying fabric for projects.