1) Download a free image editor like Gimp or Paint.Net & learn how to recolor an image.
2) Or just replace the image by exporting the one at Buttons, Boxes, & Controls > Progress Bars > Normal > MoveOverlay and importing it to Buttons, Boxes, & Controls >
Progress Bars > Normal > MoveOverlayVertical. That would be easiest.
3) If you didn't want the effect at all you could replace it with a transparent image.
4) Or you could attach your msstyle in a zipfile and I'll fix it for you. It would only take a couple of minutes.
5) You'll find examples of chunk here:
https://www.vistastylebuilder.com/forum/index.php?topic=1487.0