And that's because of this wonderful community that I prefer getting 500 credits from a NPC than try to sell for 500k to a player.
Then state what server You are trying this on. Pink purple crystals do sell on the GTN On shadowlands just fine. More recent crystals are bugged.
As someone else asked, are you allowing the temp binding to wear off before trying to sell? And not being able to sell a revan mask is simply not possible. People have gotten suckers to by the revanite saber for 100k or more just because of the name.