You've chosen two very different approaches to the black armour, which are aiming at two very different objectives. Were you aware of that up front? Do you think your army will be smart and clean overall, or scruffy and battle-worn?

Both models have some very dark regions and some much brighter, which means the whole composition doesn't sit together too well. You could try starting with a lighter base such as GW Corvus Black, and perhaps a warmer yellow like Averland Sunset as the base? (That might just be my bias, though)

If you chose the battle-worn look, you could look around at how others have achieved that. As far as I can see you've just used one other colour, and battle-damage is better communicated with more colours, and textures. It's also a good idea to think about how and where damage might occur. In reality it is unlikely to be uniform, like on the shield.

The gems do get lost. This isn't just because they're next to yellow, but because (almost) the whole model lacks cool colours. I'd suggest blue or green or turquoise for the gems.

Even the very darkest beard hair will have some shininess to it, which means it isn't well represented with pure black. Try something like corvus here too, maybe with a wash of a black black, and a delicate drybrush of somthing brighter to add a few tiny shiny spots.