I associated the suit of Pentacles with the ancient element of Earth. The cards of the suit were to always portray that in some way: standing stones, pennies on a figure's eyes representing burial, etc. For the ultimate expression of the suit, I figured the Earth itself would do nicely.
Coloring the image was fairly straight forward. The only element that had to be created was the shadow on the earth. The hatching in the clouds of the original just didn't darken them enough.