I used purple onions for one and yellow for the other, but if you guess which produced each piece of fabric, you will probably be wrong. The top fabric came out of the pot with the purple onions and the bottom one from the yellow. I was pleased with both colors, but the bottom one has a much stronger personality. The color surprise may be due to the amount of skins used: I didn't have as many purple skins so I will have to try again some time when I have had reason to use a bunch of purple onions and see if the color intensifies at all.
I am not sure how colorfast these are. I did end up trying very hot water and synthrapol to get them to stop running but never fully succeeded so these are not candidates for any project that involves water. But I felt quite environmentally righteous as I finished up by composting the boiled onions.
And, if you are still with me, thanks for the company on this natural dyeing adventure!