set colormap to change linearly between different points on point cloud?

i have a 3d point cloud on which i have to plot different points and want the color denisty to change linearly according to the points location. I have tried different commands but i have not been successful up til now. I have attached a picture in which you can see that i have made circles on the forehead, but i want to plot like 17 similar points on the face and i want the red color to change from light to dark according to points on the skin. Need some expert advise from seniors. I have attached the ply file of point cloud below:

Download Ply File </matlabcentral/answers/uploaded_files/46288/skin%20pic.jpg>