Sorry, but foreground and background color are not primarily a function of your shell (or .cshrc), but of your terminal emulator. I have no idea what terminal emulator you are using, but all the ones I know of allow adjusting the colors. Look for "settings" or "tools" menus.
If you are running on the FreeBSD console: There are kernel tunable values for the default colors. Search the forum for them.
You are aware that programs can change the foreground/background color within an 8-color setting, by using ANSI escape sequences? So changing your color using just the prompt is likely to not have the desired effect, once you start a program such as emacs or vi that will change colors internally. Please learn about ANSI escape sequences (they tend to be of the form "ESC [ 31 m"), and understand how VTxxx emulators set colors.