Another thing to consider with a candy paint job: at least in our case, a layer of silver paint was applied first. Then the gold (or blue or whatever color) is applied on top of that. The more coats of your color that are applied on top of the silver, the less bright your finished result will be. In other words, you can affect the paint's darkness by applying more coats.
Another point specifically about reds:
When we bought our house about 17 years ago, we painted the kitchen and one other very large area a Tahitian red color. The guy at Home Depot handed me a can of Dark Gray primer and told me to use that instead of the usual white-based primer. He told me to use the dark gray as a base or else I'd have to pretty much double the number of coats of red to get the same result.
So I bought the dark gray and put down 2 heavy coats of paint and the color was exactly what we wanted. Well, it just so turns out that Kelli's aunt & uncle were having almost the exact same color painted in their kitchen around the same time. When we went to their home about a month later, I commented that our kitchens were now the same color. Kelli's uncle Dave commented, "Yeah, we felt bad because the painter did it as a fixed price bid and did a really good job. But it took the poor fellow 12 coats of paint to get the red color just right. The first 3 coats, it looked Pepto Bismo pink." I just looked at Kelli and we both smiled because we knew that fellow from Home Depot had saved us some trouble.
So, if you're going to paint a bike a red color, the darker gray primer or base coat will make it easier to get the shade of darker red you're going for.
