I recently was looking for some red and blue fabrics in my stash and realized I had very little. I was actually surprised but then in reading your question I realized I've not used those colors much at all.
My favorites would be: Purples, oranges, mostly brights. I do also love batiks and have a large range from darks to lights.
Looks to me from the response that Purple is one of the top picks. Let us know when you tally?