Green dragons are more traditional, more organic and natural. They're creatures, not necessarily magical, but if they are, they're "one with the magical world." Most medieval tales or stories I would picture Green Dragons, like Beowulf. Earthsea I picture Green Dragons.
With the exception of Orm Embar, who I pictured as red. Red is either like a royal Dragon, or an explicitly fire Dragon, or an evil dragon. Maybe a mystical magical Dragon would be red. Smaug was red since he's, regal, magical, and evil.
My preference, based on what little I know about your level, would be green.