I want to know the answer to this as well. I really want purple crystals available. What's really baffling with all this crystal restrictions, is that it's not just Jedi using them.
Why can't a dark sider use a blaster with a blue bolt?
Or a light sider have a blaster with a red bolt? You know, like very blaster in the movies.
Crystal color should be fully customizable with no alignment restrictions. All of the primary 6 colors (red, orange, yellow, green, blue, purple) should be craftable by artifice starting at level 10. Variants (turquise, light blue, black core, white, etc) are fine to be rare rewards. But the basic six colors? come on.
Why this wasn't done from the beginning makes no sense.