Black / Stealth Suit colors?

I want to use a lot of chaos black to get a stealth suit look, but I don't want it to be too boring. What would you add to a mostly black color scheme to get that stealth suit look?

Example:

The picture you posted shows the most important points very well.

1. Keep in mind, that in real life black almost never looks like 'the black'™. Different pieces of black clothing for example look different, although they are all black. That is because most blacks actually are very dark blues and greens, gray on the other hand is rather rare. You can see this in your picture, because the suit has a blue-greenish tint to it.

2. The most important part about black is texture and structure. When painting something black, it is very easy to loose or suppress the the structure of a miniature. As you can see in the picture the suit has a lot of elevations and recesses. It is important to emphasis those by shading and/or highlighting and this will be easier, if you keep in mind #1 and don't use pure white-black grays, but put some blue or green into the mix.
Another important point is, that black shows structures more prominently than lighter colors. This is, because a reflection will almost look the same, but the contrast is higher. A glare on a glossy surface for example will look like white. On a white surface it is almost not visible, but on a black surface it is a great highlight.
So black is very unforgiving, when it comes to minor slip-ups or laziness.

3. Another important part is lighting. Because reflections are much more important with dark (and glossy) colors it is very important to make sure the lighting looks plausible. In the picture you can see, the the parts of the suit that are illuminated look very different from the parts in the dark.
So make sure to decide beforehand what parts will be dark and what parts will be exposed to light, because if you just highlight the whole miniature the same it will look very strange and unrealistic.

4. Last but not least: Even if you followed all those advice and made no mistakes it will probably still look dull and lifeless. That is the point, why it is important to add additional details, like metal parts or colored elements, like the helmet, the red lights or the band-aids in the picture. Just be creative, but don't overdo it, or the 'blackness' will be lost. Like in the picture, two to three additional colors, that are added at different places all over the miniature will suffice to break up the black.

Tiri Rana has some very good points. Painting such bodysuit black is really all about being on your best with highlighting and understanding of how lighting works on your miniature. Just as important is choosing the shade in which your black will be, perhaps even alternating with several shades like grey, blue, green or red, then work on as smooth as possible blending between those colours and black.

It's tricky and would probably work best if you looked up some miniatures to draw inspiration from.

You may even want to start with a really dark grey as your base instead of pure black. That way, you have somewhere to go if you want to add darker contours and shadows.

I want to link a tutorial of painting a Black Templar - there is neet things about painting black.
https://www.youtube.com/watch?v=IDxeZE6Ozds

My advice for getting that effect is washes. When I do "Black" I base coat in Chaos Black, then I pick a second color, (usually purple for my aesthetic taste) and Ink wash over it two or three times, till you can just start to see the color on top the black. Then do your detail work for buckles snaps Etc. Then Gloss coat it. The gloss brings out the color where light reflects but in the shadow it still is black.