I have had the same issues with Tiny MCE when trying to change the colors. The problem is changing colors in text is old school because it relies on the <font> tags that are mostly extinct these days. Usually that sort of thing is done in the CSS today. So I haven’t had good luck trying to get WYSIWYG editors to work properly with those tags inside a CMS environment. Try using the CK Editor plugin. I know that one handles colors and it has worked for me changing colors before.