In incomplete dominance, neither allele of a gene pair is fully dominant over the other, so the heterozygote shows an intermediate (blended) phenotype rather than the phenotype of one parent.

The classic example is the four o'clock plant (<i>Mirabilis jalapa</i>): crossing true-breeding red (RR) with true-breeding white (rr) gives F1 that are all pink (Rr) — a colour intermediate between red and white.

This differs from complete dominance, where F1 would look exactly like the dominant parent (red), and from co-dominance, where both alleles are fully and separately expressed so the flower would show distinct red and white patches, not a uniform pink blend.

Hence, a pink F1 from red × white true-breeding parents is a case of incomplete dominance.