Because they are rare, or they simply indicate what ID finds them.

Maybe they're just ultra rare? ^^; I dunno, I thought a Sealed J was normal so I 'm probably wrong...
Never seen anyone do that... unless they're doing that with multiple weapons. Ancient Saber is just a rare like any other... unless someone named an S-Rank Saber "Ancient Saber" and are just writing it in red to suggest that it's an S-Rank.
No one here really uses different font colors when typing at all, unless its one of those things where they post all their posts in that color (ex: God-IX does all his posts in a blueish color). We just all type out the names with the first letter capitalized and in the default color. Why? Because we're too lazy to do all the work just to type a rare's name like
DISKA OF BRAVEMAN when we could just go Diska of Braveman.

Why not orange

or macaroni and cheese!
I oughta' smack you for that blatant spam......
This thread is kinda spammy and not really needed :S