Why does my red ear slider not have red ears?

I just got a baby red ear slider about a month ago, but the funny thing is it doesnt have a red ear.
I looked up the image of red ear slider and my turtle looks just like red ear slider. My friend even told me that it was a red ear slider. Please tell if my turtle has a disease or some problem. I feed him dried shrimps. I have a basking area, 2 inches of water, basking light, and a plastic tank(pretty big too)
 
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