I think I might try density white this time around for the greyboy then when I obtain a clearboy and I will get green. I mean its easy to remove the backlight right and swap another?

I personally have had no issues swapping backlights. It's easy as pie.

I'm fairly certain I've installed every color backlight available. The only two colors that I feel are the most illegible when using a gameboy are red and blue. The color of the LED seems to evenly tone everything.

If you do use these colors I recommend the use of an inverted polarizer film.

Haha, and of course red and blue are the colors I chose to use.
I don't really mind using the blue one though, my eyes do get a bit tired after using it for a while but I have no idea how it compares to other colors.
The red one on the other hand, every time I look up after having been staring at it for a while I feel exactly like this: http://youtu.be/IbVmxkVC5kc?t=47s

If you do use these colors I recommend the use of an inverted polarizer film.

That's just for video cameras and other equipment. I'm referring to your eyes adapting to night. Green is one of the worst ones for this.

Thought about the wrong 'night vision' then. Cool.

Anyhooow. I forgot to mention this, but I think it also depends a little on what line of backlight it is. For example the "Envy" line that nonfinite electronics carries is ridiculously bright. Some colors really hurt the eyes. I only have two V3 backlights but they are both a lot easier on the eyes than the Envy backlights. I'm not saying the envy backlights don't have fantastic results, because they do. But if your eyes are to any capacity sensitive then they are pretty much hell to work with.

I would think that red had the least strain on the eyes. Red lights are used in the military to preserve night vision. I guess there's variables, but red is probably best for the nightowls.

Isn't night vision green? Because the human eye sees more green hues than any other color?

I'm sure it varies, however. All I know is that it had the same reaction on my eyes as if I would've been staring into the sun for a while. Huge, blue imprint on the vision that of course dissipates after a while, but not anything you'd want to inflict on yourself voluntarily IMO.

Now I'm stuck on the debate of green or orange

Was a old V2 Backlight (2 LEDs, left side), had the best contrast i ever saw.
Sold this one.

I also never really liked Yellow or Orange Backlights.