This is how I did it. :)
I removed all of the layers under the colour (also erased the other layers apart from the parts related to my kitties.) This removed the background and shows the Oekaki grey and white squares.
Then I change:
oekaki/image/image.php?id=4003324&size=large&format=auto&rev=1648979379
To
oekaki/image/image.php?id=4003324&size=large&format=png&rev=1648979379
Which gives you the empty background -
Maybe this is useful if you ever want to do this? :)
