I rarely employ any blue at in my black processes.
I tend to go by texture. For cloth I add a Bubonic Brown type of colour, a yellow-ish off white kind of thing. That gives me highlights that seem natural enough for organic material like cloth.
For artificial stuff, like sci-fi plastics, I juist go with pure grey. It looks suitably artificial.
For leather I favour adding in a modicum of Regal Blue. If only as it evokes the colour palettes of Underworld/Batman and certain high-contrast photography where black leather gets a blue tint.
For most other black, I just highlight with P3 Coal Black. It's a kind of dark turquoise. Adding white takes it all further of course, but it works as a black highlight because, try and think of something that's dark turquoise. Nothing eh*. So when we see a black/turquoise thing going on on a mini we dont have a mental catalogue dragging us away to references we have stored. If we see a black/blue we can think "oh, that's dark blue" instead of a highlighted black. We dont get that with dark turquoise.
*except for black tattoos that have faded.