Just a thought, but for working out the light vs dark sea grey color, or any other colors, you could build the model up to a point where you have a “good enough representation”, take a series of photos of that model, then mess with the colors in The GIMP or whatever graphics program you want. That way, you can try various different shades and combos top and bottom, etc. to your heart’s delight, for example using the flood fill tool. Another advantage of this approach is that if you suddenly decide you’d rather do one for a desert world, it’s simple to try various other colors. Cheaper than buying paint and trying it that way, too.
Just a thought, but for working out the light vs dark sea grey color, or any other colors, you could build the model up to a point where you have a “good enough representation”, take a series of photos of that model, then mess with the colors in The GIMP or whatever graphics program you want. That way, you can try various different shades and combos top and bottom, etc. to your heart’s delight, for example using the flood fill tool. Another advantage of this approach is that if you suddenly decide you’d rather do one for a desert world, it’s simple to try various other colors. Cheaper than buying paint and trying it that way, too.