Saga General Theory of Lightsaber Color

Ventress has yellow saber in Dark Disciple.

 

Fair enough. She didn't make it herself though - but bought it on the black market:

http://starwars.wikia.com/wiki/Ventress's_lightsaber

raising the possibility that it is simply half of a Temple Guard's lightsaber.

 

Just based on the design of the saber on the DD cover, the saber looks nothing like the uniform Temple Guard sabers:

 

Good point. The other possibility (besides the conventional "ordinary Jedi just randomly get yellow blades occasionally" assumption) is that, like Ahsoka, she attuned it to herself when she got it, and it's yellow for the same reason Ahsoka's was white - she's a Force User, and not a darksider (at least not any more) but she's not a proper light side Jedi either.

 

Ashoka's shoto was a yellow-green, so a hybrid color? lol.

Karbin used a purple lightsaber, so that color did not appear that rare either apparently, not likely to be Mace's. And Morit Astarte used a yellow blade. But the colors seem to be only change when actually holding the crystal in your palm and using the Force ect, lightsabers will remain whatever color they originally were no matter the user until somehow altered.