One of the issues that comes up with ColorDMD is the relatively poor contrast (i.e. washed out black levels) compared with an LED or plasma display. The issue actually isn't that the LCD isn't capable of good contrast, it's that the viewing angle as it's mounted in a WPC game isn't what the manufacturer intended. On a laptop computer, you always tilt the screen back until it's facing you to get the best picture, not at 90 degrees, which is what you get on WPC panels.

The solution is rather simple, angle the LCD so that it's facing you, rather than your belt buckle.
The mounting instructions has us mount the short white spacers first, then the ColorDMD, then the tall black spacers, then the hex nuts. Keep this mounting order for the bottom screws, but for the top, stack the black and white spacers and then put the ColorDMD on top. You won't be able to get the hex nuts on, so you could simply reverse the order of the black and white spacers, but you wouldn't get as much angle. I find that it's plenty secure with just the bottom nuts, and the angle is helping to hold it in place anyway.

EDIT: I added rubber washers to the stack and the picture is even better. Awesome! No room to angle it anymore than that.

Stack black and white spacers underneath ColorDMD
ColorDMD mounted at an angle, top nuts do not fit

The results are very noticeable, even by my camera.

Original viewing angle
Improved viewing angle

You'll also need to perform a -1 vertical adjustment on the ColorDMD.
I also found that to get the entire panel in and out of it's resting position in the backbox, you'll need to open the light board panel.

It would seem that newer Sterns with the tilted displays already have this problem solved for you.

I added a rubber washer to angle it back a little more and it helps even more.
It seems the shorter you are, the better the picture will be. I'm about 5'11" and it's not quite inky black but certainly acceptable now. My older display from 2 years ago is definitely better but now they're much closer. I couldn't do the vertical adjust on the old display but it has old ROM code, need to update.

Rubber washer added on top of stack

It's very snug with just the bottom nuts attached. The only problem I thought about is that it might collect dust on the screen eventually, but probably being in an enclosed environment it won't be a problem.

My STTNG doesn't and I just upgraded, but my IJ does.