We explore the relationship between general eggshell colour (background and spots) and proportion of surface covered by spots on the eggs of blue tits Cyanistes caeruleus and several variables reflecting female health and condition. Females laying more spotted eggs showed a poorer body condition, higher cellular concentration of the stress protein HSP70 and marginally lower total immunoglobulin levels in blood. In addition, these females were paired with males with higher levels of HSP70 and lower concentrations of immunoglobulins. We interpret these results based on the properties of the eggshell pigment protoporphyrin, which is known as an inductor of oxidative stress in females. Although observational, this study presents, for the first time, clear evidence of eggshell spottiness and general colour as indicators of general condition and stress in avian populations.