If you’ve ever run into this annoying little Illustrator problem, it can be very frustrating, but it has a simple fix. Every so often you may find that no matter what color you select, Illustrator converts your selection to grayscale…

Why? Well if you open your Color palette (Window>Color), you’ll most likley find that it’s set to grayscale. (like below)

All you have to do is set your color palette to something else, like RGB or CMYK. Now you’re good to go. Personally, I have no idea why this problem has made it all the way to CS4. If I wanted to fill a shape with a gray, I’d choose a gray.