If you follow @MatrixHaircolor on Instagram, you know they love to provide suggestions for formulas that can achieve the shades being sported by some of Hollywood's loveliest.
This blonde-to-red change on Emma Stone can be closely approximated with this Matrix formula:
7WN + 7GC 10 volume on roots
8C + 7GC (10 volume) on ends
"And don't forget clear if you want it lighter on ends."--@MatrixHaircolor