color changes

I have just moved from FCK to CKEditior, I used it on a site I'm developing for a client and their having a few problems. The main problem is that sometimes when they create a post, the editor is adding colour changes to both the background and the fonts, I have only allowed basic editing features so the user has no control over colours etc. the editor seems to be adding a white background and black fonts, but not every time. This is a problem as the site is using a red background and white fints. The other issue is when creating a link, if you continue editing after creating a link the new text becomes part of the link and you have to fiddle around by pressing space several times and then using the cursor keys to get back to the end of the link and backspace the extra unwanted text ? I hope this makes sense to someone and that you can provide me with some info / wisdom etc.