What do you think about adding red LEDs under the car or under the hood to a RS 1.0?

That's going to be a big NONO in florida unfortunately. That's only if you run them on the street though. It's fine in parking lots, shows, etc.
I think that it would look alright if you centered the rest of your color scheme on red. I'll be putting blue ones underneith the car and blue cathodes/LED's in the interior (another big NONO in florida unfortunately).

Do it! I did it to my BCP tC. Definetely an eye catcher at night shows.