This pattern of inheritance is quite different from the ordinary Mendelian genetics where there is one dominant trait that completely covers up the expression of the recessive trait. For example, in "normal" inheritance, if R was red and r was white, RR would be red, Rr would be red and rr would be white. In the picture you shared (codominance), we see the following pattern: RR would be red flowers, Rr would be red and white flowers, and rr would be white flowers.
