Well, I have bought several things online... basically because I couldn't find what I needed in my small town and shipping was cheaper than gas prices to drive to the nearest large city! Also, I figured I would NOT try to specifically match something up based on the color on the monitor. Now, having said that, I was looking at some charm packs by Moda for a baby quilt I made... I was under the impression that the base of the fabric I was looking at was white, but when I got it, it was a cream color. My mistake for not asking the seller specifically about the color.
Anyway... I have found some great deals on Ebay and here on this board, too! When in doubt, ask for color descriptions / comparisons!
Good luck!