This is a problem that several others have complained about - you're not
alone!  There doesn't seem to be a good way to do anything to change it using
Excel 2007's 'native' settings.  You can try changing the color scheme, but I
personally don't see much improvement using any of them.

However, you may try Chip Pearson's RowHighlighter add-in and see if that
doesn't give some relief:
http://www.cpearson.com/excel/RowLiner.htm
Yes, it says for 97/2000, but I believe it'll work in 2007 also (although I
haven't tested it in 2007, guess I should one of these days).