Keep in mind that the "plasma blade" is not an opaque
object, neither green with a white highlight in the middle, or white with a green outline, but a volume of
transparent gas that
glows green:
- It is transparent all the way to the center, but of course more transparent near the edges where the plasma has less thickness. The right kind of compositing is addition, not normal alpha blending; light absorption, and thus opacity of the blade, should be negligible.
- It cannot have outlines, unless you want the forcefield that contains the plasma to be somehow visible outside the blade proper. (Sparks etc. where the blade touches a target could act as temporary and partial outlines, making blade shape as clear as if outlined in a traditional way, particularly in the case of crossing plasma blades.)
- There are two physically reasonable colour choices for plasma light: strictly monochromatic (specific excited states of specific substances), fading through all tones of green (or another hue), from very dark to very light, but not white; and black body radiation (any gas at very high temperatures), which for all practical purposes should be white, fading to grey.
- Unless it's intended to be a toy weapon, the tip of the blade should be pointed rather than blunt and pillowshaded.