Quality of the earrings

I bought 9ct gold earrings from sterns in newcastle mall last year... Last week I went to do my hair at a salon,,, and I had to go under a dryer... Boom! my earrings turned black. I am seriously questioning the quality of the earrings, I mean I paid R800. 00 for earrings for them to turn black in under 3min in the dryer...