Sorry for late reply,
I gave you the wrong image # it is #906 sorry.
I have a hard time with resource hacker so I sometimes use Anolis Resourcer - Resource Hacker Software - Anolis
You cannot edit a theme when in use, Switch to a new theme then logoff/logon then do the following.
Open the Ashtray.msstyles
Click the + at "IMAGE" and scroll down to 906 click on + click on 0 then click on Export and Save the image to your desktop.
Edit the image with image editor (Gimp, Paint.net, Photoshop) it a 1px x 1px image.
Click on Replace then Browse in the open window make sure it is set to PngImage (*.png click on the image you edited on click Open, then click Load then OK.
File > Save