In the interests of science, I threw Banshee into the Arena - but he also uses yellow magic. I can't check Light specifically as she is on the breeding den, but I will later. I am pretty sure that the Diamond magic is for Diamonds only - I've never seen it on any other dragon that I recall.
Harvest uses yellow as well, but then he is a white/yellow dragon, so I wouldn't have thought anyone odd about that probably, however we can now say that Jigsaw, Banshee and Harvest, all dragons with White as their first colour/type, all use yellow magic.
I should clarify - when I say yellow magic I am looking at the colour of the icon, not the actual colour of the magic strike, which if Laserlight follows the above pattern, looks white on the screen. I just came up against him!