First, you will really get better results with gray backgrounds instead of white. Not only will white always look a little pastel, but it will bounce the color back onto your model, and on the walls of the room and then onto your model, and may not be flattering. And gray won't take as much power to get the same effect as black, but black can give you a nice effect if you don't light the whole paper. If you feather the light off to one side, or concentrate it in the middle, it will fall off to black, as opposed to a deeper shade of the same color.
Second, not all colors gel the same. As you discovered with blue, the intensity of the blue will vary widely from deep to pastel with just a minor adjustment of power (or exposure). Red however, will stay pretty much the same, unless you adjust the power in extreme levels.
Third, go back and read the three posts I made on this, they might help you understand. Go to the GG search window and type "Pearlman Gel Gray" without the quotes, select the "And" perimeter, and go back three months. You should find all three posts I wrote on this subject.
Remember, the most important thing is to get some distance between the subject and the background, or at least keep the main light off the background.
Andy Pearlman Studio