Though this was briefly mentioned in a thread in the DIY screen section, I thought I would share my experience here, since no one commented on actually using it.
Rosco Supersaturated Velour Black ( # 6003 ).
First, I have tried numerous paints from several manufacturers ( Benjamin Moore, Behr, Glidden, Kilz, and a few others). I specifically requested the blackest formulations possible. At best, they were a chaulky black, with varying levels of sheen.
This paint is substantially different from the others. It is designed for, and has an excellent reputation in, theatrical and television production. What seperates it from the consumer brands is the type and amount of pigment. There is an extraordinary amount of artist grade pigment mixed into the binder. So much so that using the paint without dilution is a mistake. Rosco recommends a minimum dilution of 1:1, though my painter settled on a little less than that after the first coat, more like 3/4 gallon water to 1 gallon of paint.
The painter was initially skeptical because the paint seemed so thin after being diluted, but when he started cutting in he commented on how the paint obliterated the grey primer underneath on the first pass of the brush. I've done a bit of painting in my time, and I know how hard it is to paint dark colors, even over a grey primer. Clearly, the amount of solids in this paint was much higher than 'normal' paints.
We put on 3 coats, not because of coverage issues, but because brush marks contrasted very slightly against the areas rolled on. It was minor, and I would've been fine with it, but the painter was looking for perfection.
The end result was a true 'black hole'. All paint has some degree of reflectance, but I've never come across a paint as flat as this. It's like the room is coated in coal dust.
I don't know how to quantify just how black and flat this paint is, but when looking at the wall, with a bare 60 watt light bulb 8 feet from the wall ( bulb behind me), the wall is nearly pitch black. It's like a light sponge. It's as if the wall is covered in very dark black fabric (thought not quite black velvet). When the light is off, with early evening light coming through multiple windows, the walls and ceiling disappear.
With the shades drawn, even with some minor sources of light in the room from various electronics, and a light colored carpet, it's like standing in space.
So, to sum this up, here's my take on those looking for the blackest, least reflective paint you can find:
1) Use a dark primer (we used Glidden Gripper, in grey).
2) For ceiling and soffets this is a no brainer. It doesn't get any better than this.
3) For walls, it depends. I don't have kids or unruly guests, nor is the room 'multipurpose'. I'm not too concerned about what the room looks like in full light, though it looks great right after painting, even in full sunlight, but that will change as the scuffing that all very flat paint is prone to builds up. In anything but full light however, scuffs disappear into the inky blackness. Also, I've discovered that the wall can be gently wiped with a black t-shirt with no scuffing, and in fact removes scuff marks.
4) If you can spray, you'll get away with using much less paint (1 coat is not out of the question), since multiple coats won't be needed to hide roller and brush marks.
5) Despite the $45 per gallon price, bear in mind that you have to dilute it, making the real price closer to $25 per gallon.
I considered using a 'dead flat varnish' to protect the walls from scuffing, but my understanding is that dark colors may become milky, so I passed. I'm done experimenting for now (I'll leave it to someone else). Frankly, it will cost me less than $125 including paint to have another coat put on the walls(the ceiling won't need it), and I'm willing to have that done every year if necessary. The light control, complete elimination of reflections, and improvement is the projected image make it worth it to me, though perhaps not for everyone.
I hope someone out there will be able to benefit from my experience with this stuff.