First of all, follow my old tutorial here except make the image twice the size you want: http://www.create-games.com/article.asp?id=1783

Now, convert it to 16 million colors again and resize to half the size (with a weighed average filter, bilinear and bicubic gives some kind of funky artifacting)

Wow! That's amazing it's a patterned gradient with multiple colors!

If you convert it to palette based and edit the palette entries (as I wrote in the old tutorial) you can edit five different colors. Here's an example:

Image

I took the liberty to edit in Circy's friendly grin to spice things up a little and also so some lazy bastard just don't steal the pic. Make one yourself that's why I wrote this tutorial!

If you want more than five different colors then you can start with a larger pic and resize to a lower size. Here's another example:

Image

That's 17 colors (not counting Phizzy). This was done starting from a pic of 4x size.