Maybe your home monitor is dying or it could be your video card. If you have a different monitor you can swap from an old computer, you might be able to isolate the problem.
Colin, I don't think anyone who uses the dark background does it for forms since it doesn't affect the theme colors applied to the forms. The issue with Windows and Office is that they only use children with perfect eyesight for usability testing. The problem is that the contrast between the fashionable gray text and the background is not strong enough. The smaller the font you use, the higher the contrast needs to be so the text needs to be much darker so people can see the nav pain (sic), the ribbon, and the properties dialogs.