We demonstrate the optimisation of wavelengths for the imaging of cortical haemoglobin oxygenation with broadband RGB reflectometry. Wavelengths were chosen in order to minimise the likely crosstalk and optimise the signal-to-noise ratio by simulating effects of different combinations of wavelengths on the condition number of the resulting extinction coefficient matrices. The results obtained were evaluated experimentally for four combinations of commercially available LED combinations and compared with data from the literature.