Very cool that you ripped the tileset and expanded it with the use of slopes. (Remember to give credit to FPI, though!) Also, you should do all the colors - I've always liked this tileset. However, the edges for the some of the slopes look a bit off. Below I give an example of how it should be corrected:
As you can see on the left image (without the red rectangles), I continued the pattern to cut down on the space between the pattern and where the outline of the actual tileset begins (that is, the brightest orange space). On the right image, I show which rows were altered with the use of those red rectangles.
You should consider doing that for all of the slopes, just to make it look a bit nicer. It may not be the best way to go about it, but it's at least better than how it is now, in my opinion. Other than that great work!