Colour change as a camouflage technique is utilised by both terrestrial and marine animals; however, research to date has focused primarily on rapid physiological colour change rather than slower morphological colour change. In species that exhibit colour variation across multiple habitat types, understanding how morphological colour change is influenced by environmental conditions can provide insight into how camouflage is achieved. The Endangered White's seahorse (Hippocampus whitei) was chosen as a model species due to its reliance on camouflage and the substantial colour variation observed in wild populations. Images from iNaturalist were analysed to investigate correlations between seahorse body colour and habitat colour. Aquarium experiments were conducted using juvenile captive-bred seahorses (approximately two months old) maintained in tanks with differing holdfast and tank (background) colours. Seahorse colouration was quantified as luminance (0-255 greyscale) from digital images. Luminance increased significantly in seahorses housed with lighter-coloured holdfasts, resulting in lighter colour morphs of H. whitei. Individuals also darkened when light holdfasts were replaced with darker holdfasts. In contrast, seahorse pigmentation did not change when housed in tanks with different background colours, demonstrating that holdfast colour, rather than background colour, influences pigmentation. These results demonstrate plasticity in morphological colour change and identify conditions that promote lighter colouration in aquaculture-raised seahorses. Conditioning seahorses using light-coloured holdfasts prior to release may improve camouflage within natural and artificial habitats, providing a practical method to enhance post-release success in conservation programs.