While this is not the answer, have a look in this thread regarding changing the color scheme / palette for Sense:
Bottom line: It's not yet supported, but most likely will be. In the mean time, I'm working on finding a way to change the color scheme by changing the JSON scheme that the Qlik Sense Server links to as default. That way, you could leave the default theme in place and just change the link - so that you can revert to default when needed, for instance when upgrading the Sense installation.
I'll let you know if I figure it out