First off, you don't need to invert the raw map. You just want to make the oceans the darkest parts of the map, so they will not take up a lot of your "spaces" when you make the terrain color scheme.
Here's how the raw map works. You have a greyscale image, using 256 shades of grey. I.E. every pixel in the image is one of 256 grey colors, from RGB 0,0,0 (black), to RGB 255,255,255 (white). Now when you make your terrain scheme, you enter a range, say 0.1 to 0.2, and the game selects everything in the image from that range and colors it accordingly. The scale the game uses is 0.0 = RGB 0,0,0, and 1.0 = RGB 255,255,255. So basically its a range, 0.0 = black, and 1.0 = white, and all the numbers inbetween 0 and 1 (0.01, 0.5, etc...) equal the shades of grey inbetween.
So when you tell the game via your color scheme to make everything from 0.0 to 0.1 purple, the game scans the image, and finds every pixel in your raw map that is the color RGB 0,0,0, RGB 1,1,1, RGB 2,2,2, all the way to RGB 25,25,25, and makes them purple.
Ok, back to the image itself. So why do you make the oceans darker? So they will only take up say 0.0 to 0.3 in your scheme, so you can have the rest to use for land colors. So, now that you have the dark oceans, you need to make sure your land is brighter than the ocean, so when the game scans for those pixels, it doesn't find pixels in your land area, that are as dark as the ocean, because if it did, it would make them ocean colored.
So when your looking at your raw map in an image editor, you can select all the pixels in the map that are in a certain range of color, say RGB 127,127,127 - RGB 153,153,153 (terrain 0.5 - 0.6). Thus this well tell you without trial and error opening up the game, what areas of your raw map fall in that 0.5 to 0.6 rage. So when it comes time to color them, you know exactly what area of your image is going to be made that color.
Now if you find that an area you don't want to be a certain color is going to be, you can go and brigten or darken those areas of the image so they fall within another range, say 0.7-0.8 instead.
Your Raw map will never look exactly like your planet texture. You just have to get it close to it. In fact the actual greyscale image may look radically brighter or darker in some areas than the color image of the actual planet texture because you've had to lighten or darken areas to make them fall into a different color range in your terrain scheme.
Did that help you out any???
