When I started using Game Maker, I came up with a good method for creating seamless textures with the sprite editor for my 3D projects. I would stretch it to 300% then paste the old sized image back in rows of 3 so I could use the blur feature to smoothly merge the borders of the image and then resize it back to the original size. I would make brick wall textures, grass and other things. Before I would stretch it and blur it I would pick 2 colors and use the spray paint tool to scatter the colors onto the sprite. The spray paint tool is totally different now, instead of scattering individual pixels it shoots a solid stream. It's pretty much a blurred version of the draw tool. I really wish they wouldn't have done this, or at least they could have added a scatter tool or something in it's place. It was really useful. Now, to get the same effect I would have to click a billion times to place every individual pixel.