A method for selecting a filter for detecting changes in skin color, the method comprising: selecting a light condition, wherein the light condition is associated with a spectral power distribution, the light condition including different wavelengths of illumination; determining, in response to illumination of the selected light condition, a first plurality of spectral responses for a first human perceived chromatic channel for detection of blood oxygenation, the first human perceived chromatic channel comprising the difference between signals from L-cones and signals from M-cones in response to the illumination of the selected light condition, the signals from L-cones indicating color sensitivity to long wavelengths of the light condition, and the signals from M-cones indicating color sensitivity to medium wavelengths of the light condition; determining, in response to illumination of the selected light condition, a second plurality of spectral responses for a second human perceived chromatic channel for detection of blood volume, the second human perceived chromatic channel comprising the difference between signals from S-cones and signals combined from the signals from the L-cones and the signals from the M-cones, the signals from S-cones indicating color sensitivity to short wavelengths of the light condition; selecting a frequency range from the wavelengths of the selected light condition for filtering in the first and second plurality of spectral responses, wherein the frequency range is selected such that the interference between the signals from the first plurality of spectral responses and the signals from the second plurality of spectral responses is minimized; and providing a filter capable of filtering the selected frequency range. selecting a light condition, wherein the light condition is associated with a spectral power distribution, the light condition including different wavelengths of illumination; determining, in response to illumination of the selected light condition, a first plurality of spectral responses for a first human perceived chromatic channel for detection of blood oxygenation, the first human perceived chromatic channel comprising the difference between signals from L-cones and signals from M-cones in response to the illumination of the selected light condition, the signals from L-cones indicating color sensitivity to long wavelengths of the light condition, and the signals from M-cones indicating color sensitivity to medium wavelengths of the light condition; determining, in response to illumination of the selected light condition, a second plurality of spectral responses for a second human perceived chromatic channel for detection of blood volume, the second human perceived chromatic channel comprising the difference between signals from S-cones and signals combined from the signals from the L-cones and the signals from the M-cones, the signals from S-cones indicating color sensitivity to short wavelengths of the light condition; selecting a frequency range from the wavelengths of the selected light condition for filtering in the first and second plurality of spectral responses, wherein the frequency range is selected such that the interference between the signals from the first plurality of spectral responses and the signals from the second plurality of spectral responses is minimized; and providing a filter capable of filtering the selected frequency range.