Create a colour gradient out of colour channel functions.

Input parameters:

1. ** → Function for first colour channel.
2. ** → Function for second colour channel.
3. ** → Function for third colour channel.
4. Sp → Gradient colour space.
   •  0 → Standard RGB
   •  1 → Linear RGB
   •  2 → HSL
   •  3 → HSV
   •  4 → H*SP
   • 10 → CMY
   • 20 → CIE-Lab*
   • 21 → CIE-XYZ
   • 22 → CIE-Yxy
   • 23 → Oklab

Output parameters:

1. Gr → Colour gradient based on functions.