Dark colored liquids appear to affect the coils of tank atomizers more than traditional atomizers. Further on tanks, as the liquid level goes down, the color often darkens leading me to suspect that some of the coloring stays and finally coats the coil. For this reason, when I see the liquid darken I'll often discard the last 15% of the fluid, blow out the atomizer and clean the cartridge with distilled water. Since I've gone to lighter colored liquids and done the above, my atomizers are lasting longer.
I know there are people who take their atties apart and carefully clean out whatever sticks to them. I don't have the patience. I'd sooner fill my own teeth.