Have a 1991 phillips 55 in big screen TV and the red is the only color not working how do I fix that or should I just by a new one

That unit is getting some age on it and it is past its prime. Holidays are close so TV prices should be good for a new one.

Agree with HVAC. Already 11 years old. Plasma, projection or CRT?

Some people like the older TVs better than some of the new ones. The fix depends on what type of TV you have. It could be easy, like changing a bulb, or hard and expensive like a bad circuit board. You may find one at the flea market for cheap that you can get parts from. CompUSA has good TV prices, as does Tiger Direct and some others.