https://www.mobileread.com/forums/att...2&d=1404508592
(You can download the file by right clicking the link and selecting Save target as..)
The above is one I made, but it is made with white background.
Attached is one WS64 posted that I use as my fallback suspend image in KOreader.
I have run it through Gimp2.
Try it and see if you still get those white boarders.
Luck;
Ken
P.S.; My poweroff_infotest.html:
<html>
<head>
<title>kobo menu info</title>
<style type="image/png">
p {
margin-top: 0.5em; }
</style>
</head>
<body>
<img src="/mnt/onboard/.kobo/kbmenu/txt/poweroff.png">
</body>
</html>
(You can download the attachment by right clicking on the thumbnail that links to the full sized image, and selecting Save target as..)