The most common cause of this is prog bar colors. It must use colors from the 16 color palette of the screen image.
Also looking at your preview pic, using dithering when reducing to 16 colors will look better for most images. A good free app for decreasing color is IrfanView http://www.irfanview.com
I do the prog bar and border after decreasing to 16 color, I use good old MSPaint. This way by picking colors from the screen image you can't go wrong. When you have it the way you want rect. select the 22x9 prog. bar, click edit in menu bar then copy to, put it in folder with screen image and .ini. You can then paint out the prog bar, don't need it on screen image then save the screen image.
Using IrfanView and MSPaint they both save as 16 color 4 bit bitmaps so you don't even have too think about that part of it. Gimp 2.2 is another free app that does a pretty good job decreasing colors, it also by default creates 4 bit bitmaps.
