Recommendations for navy/deep blue hair dye that won't fade to green/purple/mud

Hello all!

I have just dyed my hair with Naturtint Blue Black (Permanent). Prior to that I had salon dyed black hair on top to about ear level, and long (previously bleached) lengths dyed silver (permanent). The silver was gorgeous and didn't fade even after two months, but the black washed out to a mid brown and I had regrowth. I HATE brown and having visible roots. In the lockdown there was no chance of going back to a salon, so I decided to have a go at refreshing the black myself with the naturtint (which was closest in ingredients as the organic color systems in the salon). I did really well at keeping the dye just on the black area and didn't get any on the silver lengths, however, when I rinsed it out in the shower, the blue black dye must have washed through the silver and has turned it a navy colour with grey undertones. I'm gutted to lose the silver as I really loved that, but the navy blue actually looks really lovely! The black area has a very slight blue hue to it as well.

So, long story short, I'm looking for a semi-permanent dye that I can use on the previously bleached and dyed area to enhance the navy a bit more and make it a richer/deeper blue. The only thing is, I definitely don't want one with green undertones that is going to fade to green and ideally not purple or muddy brown either! Most of the blues described as "navy" or "midnight" shades seem to have green undertones. Can anyone recommend a blue that will just fade out to a paler blue or grey? I had a look on the fade thread but couldn't find anything suitable. Does anyone have any recommendations? I would also like to find a black or blue black that I can use on the black area to keep it nice and dark that also won't turn green! Thanks :).

TL:DR: Looking to enhance navy blue hair with a semi-permanent blue dye that won't fade to green, purple or brown. Ideally a true deep blue that will fade to blue or greyish blue (if that exists!). Also a recommendation for a black that won't fade to green. 🙂 TY.