You should read the link I posted in the sibling to your comment[1].

You may personally feel that light-on-dark is better, but your visually-impaired users will disagree. This includes a huge number of older users, as eyes deteriorate significantly with age (even among people in their 40s and 50s).

Also, you have no idea whether the complainers are in the minority or not. The people it bothered probably didn't stay long enough to figure out how to complain. Do you get compliments from people who say that they're glad you use light-on-dark?

1. http://graphicdesign.stackexchange.com/questions/15142/which...