Two new clients came to see me at Belle de Jour Salon for a haircut, both of them needed their color done but they were just coming in for a haircut. One of them had such extreme roots it was hard to consult on the haircut without first addressing her hair color.
Sometimes roots are cool. A lot of mega-blondes prefer their hair color a week after they have it done because they like the depth of the dark new growth.
I chose this picture of Julianne Hough to show when roots are good and when they are not. Basically anything up to about 1 inch of new growth can be cool. Then you get to the 2 inch range and it just looks bad, like an abandoned plan. Then you go a little longer and get into the 4 inch range and you are back to cool with an Ombré look.

I played again in Photoshop with beautiful Julianne Hough’s picture. I took her makeup off because it is my experience that clients with grey-ish/greenish don’t usually have perfect makeup on. FYI this color mistake often happens when darker haired women try to go megablonde at home with a one step color, they choose an ash color with the hope it will be a pretty and cool toned blonde, but if the ash color grabs on the already blonde ends it is an ugly grey-ish/greenish color which exaggerates bad skin tones and flaws as you can see in these images.