Light ash brown 6A is lighter EDIT: Since the first two people said 6AA was lighter, I will explain why that is false. A stands for ash, so the 6AA means it has a higher concentration of ash, which is a cool colour. Cool colours as a rule, are always darker, so since the 6AA has a higher concentration of ash, it will be darker than the 6A.
Light ash brown 6A is lighter, it contains less ash. Ash is a cool colour, meaning higher amounts will make the hair darker.
Exactly why is everyone with blond, why can't you just have jet black hair with some blonde or blonde hair with some jet black hair. Today you don't have to choose.
Although they are both the same level the 6AA will be slightly lighter. It might also be a bit greener depending on your current color. The A stands for Ash and on a lot of peoples hair it casts a hint of green. I rarely use ash colors for that reason.
As a colorist, general rule would be the 6AA has a stronger concentration of ash (the double A's) Ash always appears darker. The 6 is the level of darkness which are the same. With the AA containing more ash that would appear darker.
