you want blue.
Red requires a decent amount of heat to remove. Green is the same as red except you use it when parts are already together.
Im pretty sure the reason it says the red/green are better for small screws is because after you apply heat, it takes nothing to take apart. The blue takes a little more force to remove so you have the possibility of breaking/stripping the hardware. With gun stuff, blue isnt a problem. For softer metals, you wouldnt want it.