Marine construction replaces natural habitats with built structures of differing complexity, orientation and material properties. To mitigate resulting impacts to biodiversity, habitat complexity can be eco-engineered into built structures. However it is unclear how simultaneous modification of material properties might influence benefits to biodiversity. Substrate brightness differs between natural and built surfaces, and can influence settlement, camouflage and, particularly in the intertidal, temperature. We assessed how simultaneously manipulating the complexity (flat, complex) and brightness (white, grey, black) of concrete panels on seawalls influences benthic community establishment. Panels were affixed to high and low intertidal elevations of three seawalls in Sydney Harbour, and censused over one year. In general, effects of habitat complexity and substrate brightness were independent, and varied with site, elevation and time. Effects of substrate brightness were strongest in the first 3 months of the study, with greater colonisation of white than black panels, particularly in the low intertidal elevation of the hottest sites. Effects of habitat complexity instead strengthened after 3 months, with greater species abundances and richnesses on complex than flat panels, particularly at the low elevation. The high spatio-temporal variability in effects highlights the need to match eco-engineering interventions to site conditions and biological processes.