/usr/share/afterstep/backgrounds/DefaultTexture.mini is in afterstep-data 2.2.12-6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | <composite op="add">
<gradient width="$minipixmap.width" height="$minipixmap.height"
colors="BaseDark BaseLight" angle="45"/>
<img src="tiles/SimpleTexture" width="$minipixmap.width" height="$minipixmap.height"/>
</composite>
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