Explain the difference between simple dominance, incomplete dominance, and codominance

Simple dominance is when one trait is always dominant over the other one. Like brown eyes are dominant over blue. So if the allele for brown is present, they eye color will always be brown. 
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Incomplete dominance is when the two traits mix. Like in flowers, if red and white are incompletely dominant, then the offspring would be pink. 
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Codominance is where neither trait is dominant and both are present. Like blood type. A and B are co dominant, if an offspring recieves both alles they will have bllod type AB.