Help please - colour overlay

[torstan]

Do you have the image you are applying the map to?

[Redrobes]

I would do this with my texturer but I will tell you how this can be done with gimp like jfraz has said. I think you need to combine the two.

Create a greyscale gradient to go from light at poles to dark in equatorial regions. Then take the greyscale height image and add them together or average them or multiply them. Ensure that if you add them then the addition does not wrap around so that lowland hot areas get so bright that it wraps back to black again ! You may need to adjust the contrast of the lattitude gradient to something smaller.

Anyway the result is that you want polar regions to be cold and high regions to be cold. So that your lattitude map is equivalent to adding extra height at the poles OR that the height map adjusts the temperature so that its colder in high regions.

So once you have the two gradients modulated together then apply the greyscale gradient fill so that cold is white through browns and then greens to sand colours where real hot for deserts.