QUOTE (Holder @ May 30 2012, 02:06 AM)

Image>Mode>Indexed color...
It'll then prompt you that it'll flatten all the layers, and then present you with this box:

Make sure there's the limit of 256 unique colours set in there and for the Palette is Local (Selective)
I added a rainbow mix of colours to show you the sort of results you'll get if you have too many colours, if you're not happy with how it looks when the colour is limited try messing on with the Dither options.
Ok something new so I tried it, I followed those directions but they were already set on all those until I got to the Dither options, the Dither was set to on, so I turned it off to be like your sample. Then I just saved it as the default bmp file and tried to put it ingame, it wouldnt show up in the preview and when I tried to import It said stream line error.