how to change a "mesh" in a MapGrid


I have a List with x,y Coordinates and associated values.
0, 1, 567
0, 2, 345
0, 3, 432

x, y, value

Now I am trying to plot this List in OpenGL. I’ve found MapGrid2d. It would fit perfectly, however how could I go through my MapGrid to change the color of one mesh. (The color depends on the associated values).

I have not found a foreach command or something similar.

Thanks for your help.