Well, if you're a fan, it's can be as phabulous as your sense of esthetics. I've seen tacky RGB and very tastefully done lighting.
I looked it up on Amazon: 1 set of (2) LED strip lights goes for about 15 USD and up. So, that's generally affordable. But RGB can be incl. on just about any component, even your power supply. For a Corsair bronze 750 watt, I saw it add about 5 USD to the Amazon price, for eg.
Personally, I find it tacky in general. My PC's motherboard has an RGB controller, I shut it off in the BIOS. I have my Corsair RGB keyboard custom set, that's about all I will tolerate.
Tacky imo
Tasteful imo
As far as fire hazard: ?? I doubt it would be strictly an RGB thing. If the power supply is over-loaded, it will almost always simply shut down. The PSU can be more of a hazard that way, than the RGB.