I got Mariana color variants working on Sublime Merge.
Changelog: Added alternate version with square tabs. Here are two images for comparison.
"theme": "Mariana Plus (Warm).sublime-theme",
“theme”: “Mariana Plus SQ (Warm).sublime-theme”,
Changelog: Redesigned entire theme.
Changelog: Added the color schemes in the repo. Now the theme is supposed to work out of the box.
Changelog: Fixed the diff line highlight. Thank you milkman and facelessuser for the tip.