It's darker because it's only emitting light from 1/3rd of its area when you separate the pixels like that.  Every pixel that you place for a single R, G, or B value, that pixel is still RGB, and you're only engaging one value, so it's much darker.

http://j.imagehost.org/0346/Problem_1.png

Here's what you're seeing (left), and painting (center), but with a diagram of how that actually engages the light of the screen (right).  As you can see, because the red pixels aren't engaging the green or the blue, there's a huge black gap even when representing a fairly light color, resulting in a dark image.

I guess you could put the gird on a separate layer if your program supports different layers, and once you're done with the grid, delete the layer.. at least, that might work.

removing the grid, that would be effing difficult but somehow posible??

maybe doing something with more brilliant colors will look better

the trick to it is the grid, remove the grid ^^

these sorts of things are pretty cool looking.  pretty nice, but ya if only it werent so dark somehow.

I've done some stuff like this before, it's not real hard once you set up your grid by hand you can just pixel into the negative space

is done all by hand, don't you read read the description? obviously the black horizontal lines were drawn on a different part of the canvas and then moved above the original to simulate scanlines

and the software I use doesn't have pattern fill

http://img517.imageshack.us/img517/9876/kattyntsctestdostest.png is the process and http://img263.imageshack.us/img263/9657/kattyntsctestantes.png is what it really looks like or would look like if it was really displayed on tv or a lcd monitor

hey ive tried this the other day aswell but without the interlacing....anyway... its quite hard to read... and if u rly did all by hand (like with the pen tool) that must have taken very very long.....i dont know which software ur using but another way would be 'pattern fill' which is much  faster