How I'm Doing Colour Pallettes for Games
Get your source image. This can be anything, but it helps to pick an image with some nice bold colour usage. In this example, I'm going to use a piece of concept art from the Doublefine game Broken Age.
First, blur the image until the fine details are gone, but the colours are still clear.
Change document mode to indexed colour, and from the palette dropdown, select local(perceptual).
Reduce the number of colours till it looks "blobby" like this:
open up the gradient.png file, and change image mode to indexed colour
from the dropdown, select "previous"
erase any unneeded colours from the image by filling them with the paint bucket
change the image mode to indexed again, and choose "exact"
choose "save for web and devices"
change the file type to GIF
click the little down arrow next to the colour table, and choose "save colour table"
In the top right of the "swatches" panel, there's a little down arrow.
Click that and select "preset manager"
You can use this to clear out any default swatches, and load in that colour table file you just saved.
For some cool effects, try applying your new colour pallette to photos/other game art. Here's Bastion and Offspring Fling: