Can Red Ear Sliders Be Earless?

Ok so My little Brother bought a red ear slider turtle, a few weeks back for his birthday but it seems that it has no red lines or markings anywhere on it's body... Do they grow these red designs through there lifetime or are they suppose to be born with these? Is it a yellow belly slider turtle that they replaced with the red ear slider? I need all the information and details about the red ear slider and yellow belly slider thank you all.