The color yield of the samples (Fk) was measured by
the Tex flash spectrophotometer (Datacolor), from
which K/S (Kubelka-Munk theory) was calculated as
shown in Eq. (5):
Rλ was the minimum reflectance of light with a given
wavelength (predominant wavelength) from a sample
of infinite thickness, expressed in fractional form.
The Fk function considered K/S in different
wavelengths of the visible light as well as color
matching functions Eq. (6).