Hey Mike, most likely, you're legal. I've never come across any statutes in the U.S. that require amber rear turn signals or prevent changing "factory amber" to "custom red."

I suspect the ONLY way your mod might be illegal is if the signals (or brake lights) no longer meet the requirement of being visible from ____ feet away. ("___" will vary on your local laws. ) You have painted and tinted the plastic which probability reduced the visibility. If it's too much that's bad, but if they still meet the distance requirements then nobody cares.

* Disclaimer: I'm an idiot on (and off) the internet and do not know all laws in all locations. You have paid $0 for my opinion/advice - you may be due a refund. It's usually not easy, but eventually you will find a website that details all the statutes where you live if you look long enough.