Uh, I just thought the artwork for the Pendant was for an uncharged Pendant...maybe when it shimmers, it shimmers red...
The pendant is discharged, but it was charged at first and it was there that it changed color. I think we can sum up all this like this:
- Raw Dreamstone when encountered in nature is red (ex: Ayla's Red Rock).
- People can manipulate Dreamstone to create items, it's still red (ex: the "Ruby" weapons in Prehistory, the Red Knife).
- People can charge it with magic energy, it changes color (ex: the Pendant and the Masamune when they were created).
- Those magically charged items can be discharged but they don't revert to the original red color (Marle's Pendant is yellow/blue, it doesn't revert to a red... rock).
Where Leah's gem fits in all this is anyone's (or nobody's) guess though...