Frosty i also have a Dell monitor but i build my own PC's. You should do what voxmagna said first but i would also get that monitor setting changed from "default" to the correct monitor too. Under that "ad" section you should see a bunch of manufactures including Dell. Double click on the Dell on the left and on the right panel you should see a bunch of Dell monitors to choose from. See if your monitor is listed there it mite very well be there. If it is listed pick that, if it isnt go to the Dell site and do a search under downloads at Dell put in your monitor model number, they should have a driver listed for your monitor if its not to old.
But like Voxmagna said, do what he suggest too and see if you have a color profile problem. Good luck.