Answer
Four-O'clock plant (Mirabilis jalapa) follow the phenomenon of co-dominance.
Co-dominance
Co dominance is a relationship among allele where both allele contribute to the phenotype of heterozygote.
Explanation
Japanese 4 o clock plats have two types of flower in their parental generation that is red and white. When these parents are crossed a new plant with pink colour is also observed in their F1 generation as shown in cross below.
Parental generation
Phenotype Red Flower x White Flower
Genotype RR rr
Gametes R, R r, r
F1 generation Rr, Rr,Rr,Rr.............Pink Flower.
Result
The allele contributes in the phenotype of flower and pink flowers are produced.