Fig. 4. Calculated noise-scaled chromatic distances achieved by different hypothetical L cone tuning (see Materials and methods) for the visual task of discriminating food rich (mature) from other (immature and senescent) inflorescences of Banksia attenuata, the most important measured food resource for honey possums. In this case, incrementally shifting the honey possum's L cone tuning to longer wavelengths would offer no clear advantage. For the conditions of sun and cloud, which represent larger portions of time than the dusk conditions, and for which we have many more measurements, a local optimum in L cone _max is evident close to the value found in the honey possum.