1. Yes, but for anything more than "just gets brighter on clash", you'd need to use a mixed or custom LED. For example, Deep Blue (4x Royal Blue dies) wouldn't change colors if you wire it for flash, but you could wire an Arctic Blue LED (2x Royal Blue, 2x Green dies) to have a Deep Blue (or Green) blade that flashes to Arctic Blue. Similar with a Purple module - you could have a Red (or Royal Blue) blade that would flash to Purple.
2. The NEC Spark 2 or Plecter NBv4 (Nano Biscotte v4) would be the best picks for a SF X4 LED. Both of them have 2 direct drive LED channels on the board, which would allow you to either mix or use each single color of a 2x/2x or "6w/6w" LED (as explained above).
Other boards are capable of supporting a "12w" LED are, well... pretty much all of them, to one degree or another: Plecter Pico Crumble, Prizm v5, and Crystal Focus v8; and the NEC Spark Color 2 and Igniter 2. I think a few of those (Prizm, CF8, Igniter) are overkill though if you're not using RGB. The only board that really had a problem was the NBv3, since the main blade channel had such a low Amp rating.