The fourth-order differential operator has been designed including its coefficients Bi and Ci in such a way, that its first
three eigenfunctions Φi(λiΕ) are almost identical those obtained by orthogonalising the colour matching functions x(λ),
y(λ), and z(λ), CIE 1964. This operator gives an exact description of colour perception. Any changes to the spectral sensitivity
of the cone system and Bi, Ci coefficients in our mathematical model result in a description of colour blindness in
the observer. The principal aim of this paper is to mathematically describe the above-mentioned operator.