Long lasting permanent hair dye for resistant grey hair that doesn't fade brassy?

Since grey hair has a tighter cuticle, it is quite "resistant" to pigment. So I'm on a mission to find a long lasting permanent hair dye for resistant grey hair that actually holds its tone well.

Most of what I've been experimenting for years now would only look great for a week, and then some sections start fading with these weird orangey color while the rest of my hair stays dark. Is there a specific formulation/ingredient I should be looking for longevity?