A red gel will give you something between a pink and a peach color. A blue gel will give you a light blue somewhere between a sky blue and a baby blue. I don't know about any other color gel, but have played with red and blue a lot. To pump up the color, your light that the gel is over will have to put out a lot more power than your main light.
When you see a really red background, that is usually done with a red gel shot into a black or dark red background... usually with more than one light.
When I was shooting models a lot back in the late 1980s, I played with gels a lot and tried just about any combination you could dream up. A black background with one blue light and one red light gave a very pleasing purple in the middle with red on one edge and blue on the other. Arkie