in pictures :
much likely :cc = ∑i=013 {Cos[x·Sin(y)·i]i·Sin[x·Cos(y)·i]i} , i ∈ (Z0,Z+) c = round[2(cc + 16) - 24] color_index = f(c) = {0 , if c ≤ 0 , c , if 0 < c < 15 , 15 , if c ≥ 15}
[Eop]