The "Turning green" function is a little misleading since it's based on where your cursor is pointed specifically. Since you're not often pointing your cursor directly at an enemy mech when launching LRMs, it may or may not change color properly.
PPCs have a minimum range of 90M, and will deal reduced damage at closer ranges. ER PPCs have no minimum range.
Most of the graphics config options are turned off in the launcher because they're working on implementing DX11 (Soon™, best guess 2 weeks). Advanced graphics configs can be tweaked through a USER.cfg file provided in the root directory. There was a repository on the forums for various levels of graphics settings that could be achieved with that file. I'm not sure where they were relocated to when the forums updated.
And yes, the number to the right of the weapon is the maximum ideal damage range. Most weapons (Barring the PPC and LRMs, as noted already) will do full damage up to that range, and then decreased damage beyond that range.
Example: Medium Lasers show a range of 200M. Thus, they do full damage from 0-200M, and have a linear damage decrease from 100% to 0% over 200M-400M. So, they would do 50% damage at 300M, and 25% damage at 350M.
Ballistics get a longer range dropoff (up to 3x ideal range), which also scales linearly.
Edited by Vlad Ward, 30 October 2012 - 07:13 PM.