Ah, I just had a brainwave and remembered the name. I was thinking of Iron**born**, by Olle Lindestad (who it looks like is currently working on another webcomic, "Current Culture"). The blurb:
Robots aren't supposed to be able to use magic. But Opal is, and she's as confused about it as anyone. As conflict looms between a city of magic and a city of robots, she'll have to be quick on her feet...
It apparently was "published online between 2007 and 2014"; the original website is no longer up (so I'm not sure if my memory of its having a red color scheme is correct, although the logo is red) but part of it is currently online at a different website. The last page uploaded so far is page 160, from 2010. But the author made a blog post on November 6, 2017 indicating that more pages may be uploaded at some point in the future.