The expression of visual signals such as colouration can be altered by parasitic or pathogenic infections through multiple pathways, including resource reallocation, impaired tissue structure, and reduced pigment acquisition. These effects may compromise the functions of colouration and overall fitness. Conversely, the link between pigments and immunological defences can aid differently coloured individuals in coping with infection. While the pigmentation-condition association has been widely studied in the context of sexual selection, far less is known about how pathogens affect defensive colouration, such as aposematic signals. Here, we investigated whether infection by the fungal pathogen Batrachochytrium dendrobatidis (Bd) is reflected in characteristics of the melanin- and/or carotenoid-based colouration of the aposematic poison frog Dendrobates tinctorius in the wild. Using ddPCR to identify the frogs’ infection status, and multispectral digital imaging to quantify their colouration traits, we show that neither type of colouration is a reliable indicator of Bd infection. Instead, body size influenced both infection outcomes and colouration, with sex-specific patterns suggesting potential ontogenetic or life-history trade-offs. Our findings highlight that the links between colour expression and condition are more context- and taxa-dependent than often assumed, and suggest that, in D. tinctorius, defensive signals may remain stable despite pathogen exposure.