I did a quick comb effect, with a subtle color gradient horizontally. Controller d-pad adjusts the rates of each comb. NES is recommended, as I can't test it on emulators, though I imagine Nestopia would handle it correctly.
I must say Bargg, on FCEUX and Mednafen I am getting some very interesting "tears" within the individual blocks. The edges of the blocks are perfect, but they have some kind of jagged gradienting inside of the box. I think it's just a timing accuracy thing with the emulator, and with the inaccuracies of an actual NTSC NES and NTSC display device they should be virtually unnoticeable.