The Heart of the Guardian and the Mantle of the Force are special color crystals that enhance your sabers and give them special colors. To the best of my knowledge, they are only available in the PC version of the game. Each of them alters the effects of the "effect" crystals you put in your saber (for instance, an Upari and a Solari crystal give slightly bigger bonuses when attacking dark side targets than they otherwise would have).
To get them, you have to visit Yavin after you find your first Starmap. Talk to the Rodian there and learn everything he has to say about Trandoshans. After you have two or three Starmaps, go back and you'll chase of some Trandoshans. Later, after you've collected all four Starmaps, you visit Yavin again and this time the Trandoshans ambush you. If you save the Rodian from the Trandoshans, he will sell you stuff from his secret stash. Trust me on this: if you use HK47 or even TM34, you can turn them into absolute killing machines with the gear this guy sells. He also sells the Heart of the Guardian and the Mantle of the Force. The two total out to about 45k credits. You'lll get

from the Trandoshans you just killed, but you'll also need to be carrying some cash when you arrive.
Also, the Rodian on Yavin will give you the absolute best prices on EVERYTHING you can sell him. Racing bonds that get you 60cr on other planets will get you 150cr on Yavin. You can make a huge fortune selling him gear.
