One thing to consider before choosing Violet Amethyst as the FoC color for a Guardian Blue blade (with a fixed LED):
If you choose a FoC color that isn't all that much different from your primary color the FoC will be much less noticable. Once I ordered an Orange saber with Sentinel Yellow FoC. I could barely discern the FoC with the blade flickering from orange to yellow. It seems best, to me at least, to choose a FoC color that really stands out so the effect is noticeable. I generally choose silver FoC for a blue blade and the flash is bright & obvious.
In all honesty I haven't seen a blue blade with a Violet FoC, but I would think this would produce a very subdued flash effect. If you are going with an Emerald saber this obviously won't matter since you can experiment and change colors at will.
Yea, I was first thinking on putting a Artic Blue flash of clash but then I watched videos on sabers with that and I couldn't see it but just a slight flick, but then I watch a purple flash on crash and thought it looked great!