From my classification this seems similar to base16 https://github.com/chriskempson/base16
Is this correct and would you like to clarify the benefits of using themer instead of base16? Have you considered intercompatibility by i.e. allow conversion from and to base16 themes?
One thing I will add is that I found base16 more challenging to use if I wanted to use a custom color set instead of the default ones. It was also difficult for me to tell which packages of that project were maintained, which were deprecated, and how the packages were organized in general.
Back to base16, if you'd add base16 as an input and output you'd be able to benefit both by expanding the available set of themes with those of base16 and expanding the set of output formats to those supported by that ecosystem. That would make your tool far more interesting for someone like me who's already using base16.
themer is inspired by trevordmiller/nova and chriskempson/base16.
Conceptually, themer is very similar to base16, but:
1. It is lighter, and simpler to use. 2. It is more easily extensible with your own color sets and templates. 3. It integrates better with your dotfiles, especially if you keep them under version control.