A good way to test visually a good grey or black colored/tinted prescription lens ............................

The easiest way to see if a grey or black tinted lens is fairly neutral is by holding 2 the same way tinted lenses, on top of each other, outside without the interference of artifical light and look at some concrete wall or ashphalt.

If there is a red tinge, the lens color does not have a neutral black color. Besides not giving a perfect color reproduction these lenses will also fade into a purplish, ugly looking sunglasses.

The most delicate art of tinting has never been in the optical dispensing field, but in the manufacturing of photographic filters which has been searching forever for a perfect black color that has no visible red tinge, even looking through a double filter, or will show on a spectrometer graph as a nearly straight line.

A black dye is made from a green color, of which there a thousands of variations, by adding red which makes it going into grey/black and by adding more red into brown. By choosing the different green shades, the blacks and browns can be totally different.

These days such nearly perfect grey/black dyes are now available on the market and the opticians that do their own tinting should use them, and look to find them, and the ones that get them done in a lab should check their jobs and refuse any reddish looking black tinted Rx lenses.