I think of my fabric purchasing strategies a lot like wardrobe strategies. You know how they suggest used to suggest that for suits and shoes, you have a core color, be it black or navy or brown or ivory, and then buy coordinating colors in blouses and shirts? Well, that was the advice back in the day when I dressed for a professional job every day.
So I have just a couple of core neutral colors I use, and buy in large quantities -- a true white, a true black and a certain brown I really like. I may be tempted by gray or white on white, or cream every now and then, but I try to stick with my core, tried and true colors. When I buy new fabrics, I tend to buy things that are going to look good with those. And interestingly, the fabrics that are going to look good with pure white and pure black tend to look good with one another too.
So by limiting your palette, you actually open up a lot of mix and match opportunities, and thereby save money in the long run.
That and never buy mags (web has better stuff) or books (library is free).
RST