If the same happens with original tiny widget - you should use their resources to report an issue/find a workaround. We chosen the way when we not changing original code in order to be able to update to newest versions. B.t.w currently such update in progress. So if the latest tiny version has no such issue - you will get the feature working in 3.2.2 release.
The issue is not coming for original TinyMce version.
The issue is coming only for the forecolor and backcolor feature of tinyMce in <rich:editor>
so then should be solved after update to latest version planned to 3.3.2.