Am I Colorblind???

I have all my back pieces cut and am cutting the batting now.  These are such big blocks and take up so much room that I want to sandwich and pin together the blocks I have before I work on the others. 

I lacked backing for 4 of the 30 blocks I am making for DHs quilt.  So I looked in my stash and found, what I thought, was the "perfect?" fabric.  Colorwise, it definitely does not match, but as a stand out on the back, for sure.