It's all about the color and visibility from outside the boat.
Flashing blue lights are strictly for law enforcement. If you have those blue lights on when running, and they can be seen by other boats, that is illegal. As your boat rocks and bounces through the waves, they appear to flash to observers.
A friend of mine had blue underwater lights. In choppy waters, they would come out of the water when the boat rocked. Very quickly law enforcement caught up with him, and he was issued a citation for displaying blue lights. He swapped them out for green ones.
I have run amber under my gunnels for decades now, and I have never had a problem, despite having been checked. Gentle light you can see by, and not get in trouble.
View attachment 115175
View attachment 115176