Well, there are a couple of things.
1. Did the style write? When you go back in is the new color in place? If not, make sure your styles/ directory is chmodded 777 and the files within it are chmodded 666.
2. Is the style you're editing in use? A lot of people have more than one style, be sure the one you're editing is the one you're actually using.
3. Did you use proper syntax?:
background: #f3f3f3;
color: #000000;
The style editor is a fickle mistress, if you're not comfortable with editing CSS you may want to look into hiring someone to create a style for you (there are several of us who have such services available).