For the samples coded 1, 2 and 3, both and increase with wavelength, as shown in Fig. 5. We pointed out that these quantities are given in arbitrary units that depend on the wavelength. However, the overall relative increase of and from 500 to 700 nm is much larger than that observed for the Lambertian alone (Fig. 2). As a result, we can safely conclude that the reflectivities of all samples for both the directly and indirectly scattered light do increase with wavelength. For , the trend is caused by an increase in the average number of scattering events suffered by the photons, as light penetrates deeper into the layers. This increment is larger for whole colon (sample 3) than for the mucosal layer (sample 1) because for the former, longer wavelengths may penetrate into the deeper layers (e.g., muscular and fat) and then backscatter, while these layers are absent for sample 1. Sample 2 (mucosa, submucosa, and muscular tissue) is an intermediate case. The increase of with wavelength also confirms that light penetrates more deeply.