C![custom character]() w={cp
w={cp(
ui0,ui1)|
uij∈Us, Σ
juij≤1, 
P=P![custom character]()
}??(5)
where u
i0, u
i1 are the same as in Eq. (1), and the 10 control points P interpolated by C
p are expressed in terms of the color sail parameters. These choices make it possible to express C
![custom character]() w
w in matrix form with clean derivatives of the interpolated colors with respect to the color sail parameters.