I should add lights are on about 16 hours per day and about 5" from top of tomato's.

That's normal coloration imo.

they look fine...

They are probably a little cold, which makes it harder to take up some nutrients, but it usually works itself out.

https://www.houzz.com/discussions/2197140/purple-stems-on-germinated-tomato-seedlings-infancy

Purple underside of the leaves are normal, but I'd recommend you get better lights.

Your plants are to tall and leggy and growing to look for light, or the right light. Your LED shop light is worthless for growing plants and doesn't emit the right wavelengths. Get a few florescent fixtures over them or drop a load of cash for LED grow lights designed to emit the red spectrum from 640 to 680 nm and the blue wavelengths from 430 to 450 nm. As far as I know they haven't invented full spectrum LED lights, but I could be wrong.