Advice on Loreal Color Gems

I purchased the Color Gems semi-perm in a lt ash brown (opal family of colors) to color my gray roots. (I'm using semi-perm while I ponder letting my gray grow out and stop coloring entirely.) The instruction booklet says to mix it with 50% of a color from the quartz selection, and I bought lt. natural brown. My question is: why do I need to mix these colors? The color I'm striving for is a cool lt brown with no gold or red, so why isn't the lt ash brown fine on its own? Why does Color Gems recommend this mix for gray hair? Thanks!


Edited by pasdebourre

Perhaps it's to fill out the colour a bit more.  If you think about it, grey hair is colourless/almost colourless, it needs pigment putting back in and the medium brown will do that by putting a bit of red in that you won't notice in the colour.  I may just be talking crap, but it makes sense to me