Gold Post Earrings Turned Red?

Real gold doesn't turn colors. Perhaps these are gold-plated, vermeil or some other mix.

Thats not necessarily true. Other metals are used in gold to give it strength and color (ie..white gold, rose gold) Thats why theres different carats (10k, 14k, 24k)
They refer to the mix of gold and supporting metals. The other metals like copper and nickel do tarnish and react with your body if you wear them frequently. Just give them a good cleaning with a soft polishing cloth.