A Jedi Master's Saber
After becoming a Jedi Master and building one's own lightsaber, the player is given an autoloading saber of sorts. It is a useless weapon, without any benefits in combat. The player can then take another working saber and merge it with his or her own. Then the master's own saber becomes just as powerful as the saber that he or she merged with it.
Jedi Masters can also set their saber color to whatever they wish out of the available colors they have collected. To permanently add a saber color to the their collection, the master must merge an acquired saber with their constructed handle. Jedi who have collected enough saber colors may also use rainbow.
For the Jedi Master's saber, color bears no significance to the saber's power. The saber might be colored violet, but still be equal in power to a black saber. The Jedi Master can change their saber's color at will with the <color> command.
A Jedi Master can 'unmerge' the components of the saber previously merged with their personal saber, returning the original saber to working condition. If a Jedi Master damages, fixes, improves, or reinforces their personal saber, they are really damaging, fixing, improving, or reinforcing the components of the merged saber, which will be reflected when that saber is unmerged.