Can you solve it? The colourful truth about elves

Logic with Santa's little helpers

Here's a logic puzzle that was sent in to me by a (very smart) 12-year-old.

Four elves Glarald, Mnementh, Virthana and Tinsel are each wearing tunics of a different colour. At least one of these elves is a liar. (A liar is someone who says only statements that are untrue). During a break at elf school, the following conversation is overheard: