Looks cool...but is illegal in most states. Most laws require the light to show red when on. Tinting changes the color, hence they don't meet the ordinance.
If it shows red when you step on the brake AND is visible from at least 300' in normal sunlight, you're probably OK. At least that's the ordinance here is Kansas, but most states have similar laws. Might wanna check with the local PD to be sure.
Usually it's not something you'll get stopped over, but if you become involved in an accident and have an equipment violation (even as minor as a tinted tail/stop light) you can draw unwanted liability because the other driver's lawyer can say, "My client didn't see him because his taillights weren't red." Then you get blamed for causing the crash, your insurance company doesn't want to pay, etc.
I'm not saying you shouldn't do it, you just need to be aware of the potential problems, regardless of how remote they may be.
Andy