Well I guess you're aware that red pretty much stains the inside of your radiator and blocks.
Anyway, I personally was debating the same thing as you and decided to just go with distilled water, but used red LEDs in the correct placement to give my reservoir the same effect you're looking for. I like this option a lot and I'm able to just change LED colors if I want to change my color scheme in a new build. I'm also using primochill red translucent tubing though, so having colored coolant wouldn't effect that much.
If you're one of those guys that sleep near your computer and hate LEDs at night, maybe colored coolant is the way to go, but I would only go with red if my color scheme depended on it.