Search by color
googleblog.blogspot.com
googleblog.blogspot.com
http://labs.ideeinc.com/multicolr/#
Also note that if you search for a white, then black, the url becomes [...multicolr/#colors=ffffff,000000;]. Your color choices are actually 16,777,216 - however well you know your web colors.
This can be more useful if you want a more specific hue, compared to generic 'red'. Subject matter, however, is a different issue.
ps I don't see the "All Colors" drop down in my blue bar. But you can do the same search by appending "&imgcolor=yellow" to the url.
[edit] It didn't show up on Firefox, but showed up fine when I used Chrome.