> 468
color[i_] :=
Which[Mod[i, 1] < 0.25, CMYKColor[0, 1 - 4 Mod[i, 1], 1, 0],
Mod[i, 1] < 0.5, CMYKColor[4 (Mod[i, 1] - 0.25), 0, 1, 0],
Mod[i, 1] < 0.75, CMYKColor[1, 4 (Mod[i, 1] - 0.5), 1 - 4 (Mod[i, 1] - 0.5), 0],
Mod[i, 1] ≥ 0.75, CMYKColor[1, 1, 0, 4 (Mod[i, 1] - 0.75)]]
ContourPlot[-x^2 + y + 1, {x, -3, 3}, {y, -3, 3}, Contours ->10,
ColorFunction -> (color[1 - 0.66*(#1 + 0.5)]&), PlotRange -> {0, 4}]

で、どう？