Enhancement request: ability to set trim color

[hudcap]

Thank you for this awesome project! I am in awe...

I think it would be beneficial to have the ability to set the trim color. I often deal with images that have e.g., whitespace on the bottom and the right, so the top-left pixel is not white.
Something along the lines of &trim-color=white or &trim-color=FFF, which would then be used in place of the top-left pixel's color.

Thank you for considering!

[kleisauke]

This has been implemented with commit 9ad2919, which has just been rolled out to production. Example URL:
https://wsrv.nl/?url=https://upload.wikimedia.org/wikipedia/commons/2/20/Flag_of_the_Netherlands.svg&trim&tbg=21468b
(i.e. only trim the blue portion (#21468b) from the flag of the Netherlands)

Documentation will be updated later to reflect this. Thanks for reporting this!