To add more color, try using all of the available colors (red, yellow, orange, and green) bell peppers. It makes for a pretty dish with all of the colors added to this. Try using green onions in place of yellow, though expect a stronger onion taste from these as they pack more flavor in my opinion.
Fresh peas can also be used.
For a variation, add pulled chicken breast meat to this to make it a ranch chicken pasta salad.