I've been covering my greys with L'Oréal Casting for years. I just use it on the roots and I leave it on for 40 mins (on my hairdresser's advice).
My hair is brown and I use a cool, light brown dye.
I used to do it once a month but I'm now doing it once a fortnight because it's fading so quickly.
I'm wondering if I need to switch to permanent but I don't know where to begin. Will it leave a really harsh regrowth line? With the Casting I get roots quickly but because the dye fades it's not a harsh line IYSWIM.
Any tips would be welcome. I'm especially interested in brand recommendations and whether anyone has experience mixing their own dye with Majirel.