In many taxa, success in parental care requires the coordinated efforts of both parents. Given the evolutionary potential of parental performance, as well as phenotype-related behavioural differences, it is surprising that parental coordination in polymorphic species has attracted only very limited research attention. To redress this gap, I combined multiple approaches to assess parental performance and coordination of parental effort in the colour polymorphic and biparental cichlid fish, Amphilophus sagittae, in its natural crater lake habitat. I compared parents of the two colour morphs, dark and gold, as well as pairs that had mated colour assortatively ('same colour' pairs) versus disassortatively ('mixed' pairs). The two morphs differed in terms of a higher than expected number of single gold morph parents. Interestingly, parental coordination, in terms of the size of the defended territory and the rate of aggressive responses towards natural territory intruders, was lower in mixed than same colour pairs. Mixed pairs also had their territories in deeper water. However, no pair type differences in early survival of biparentally defended broods were detected. The findings contribute towards a better understanding of the role of parental coordination in polymorphic species, highlighting the importance of considering parental effort, coordination, and performance in the context of the dynamics of (colour) polymorphisms in the wild. Indeed, if the observed behavioural differences will translate into negative fitness effects for mixed pairs, parental performance can also provide a mechanism selecting for colour assortative mating and restricting gene flow under mating regimes that are not completely assortative.