My hair is naturally mid brown, currently dyed dark red. I want to go to light brown, mostly because I've started to get more greys- they're really obvious against dark red hair and I don't think they would be if it was light brown. I also quite like my greys and when they are a bit more dispersed and not all in one odd clump at the top, would like to ditch dye altogether- and I imagine the transition to no dye would be smoother if it were light brown rather than dark red.
Can I risk slapping a light brown dye on straight over the red, or do I need to use Colour B4 or similar first? I'd going to go for a warmer light brown rather than an ashier one anyway- do you think it would work, or I do have to be not- lazy and strip the old colour first?