I just tried another 12v wall wart and it was the same story.
I'm trying it with both a genesis and an NES and I get the same results.
What is strange though, is that initially I was using a multi A/V selector box thing and thought maybe that had something to do with it. It did not. But it has these push buttons on it that actually physically go down and complete the circuit, so there's no digital logic going on inside at all. If I rapidly press the same button down the screen glitches/flickers, but at times it will show the full color for a split second. I would assume that rapidly unplugging the rca cable would do much the same thing.
Is it possible that my screen is stuck in pal mode? Is this even what it looks like when you run an NTSC system on a pal screen?
My other idea is maybe there's a grounding issue? It looks like the only ground going into the screen comes off the 12v barrell. Shouldn't each rca jack have it's own ground?