Oh, and in regards to the colour question. Amber is used because it is the colour that your brain recognises fastest - although we are only talking about milliseconds faster. However, in arid terrains, like outback Australia or Africa, there are a lot of amber colours in the scenery and the amber reticle MAY, on occasions, not stand out as much as it should.
Green is the colour range that you lose last as the light fades and my best mate swears by green as the best option. The green is noticeably different to any natural greens, so doesn't get lost in the foliage and seems to work well.
However, I prefer red, simply because it stands out like 'dogs balls' against any background/environment. Plus, and it is just a personal thing, red is the colour we have always associated with the act of shooting a firearm! Red is the colour we use on safeties to indicate when the firearm is ready to fire. Red is the colour we associate with danger. So, for me, red is the natural colour to use for a reticle and, in a way, it encourages you to take the shot.
-------------------- "White men with their ridiculous civilization lie far from me. No longer need I be a slave to money" (W.D.M Bell)