Updated 20-Sep-2023
Here are some ways of getting things tweaked. Your mileage may vary.
Mint-Y-Dark
This theme has some hardcoded colors in PNG files. Grayscale them with ImageMagick, as follows:
for file in /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/*.png; do convert "$file" -colorspace Gray "$file"; done
for file in /usr/share/themes/Mint-Y-Dark/gtk-3.0/assets/*.png; do convert "$file" -colorspace Gray "$file"; done
Edit the /usr/share/themes/Mint-Y-Dark/gtk-2.0/gtkrc file for color. Replace #8fa876 with #993333 for a nice red to go with Mint-X-Red Icons. I prefer scrollbars with 15px width.
Edit the /usr/share/themes/Mint-Y-Dark/gtk-3.0/gtk.css file for color and scrollbar width. Replace #8fa876 with #993333 for a nice red to go with Mint-X-Red Icons. I prefer scrollbars with 15px width.
Double the size of the following .png files in /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/
- slider-vert.png
- slider-vert-active.png
- slider-vert-insens.png
- slider-vert-prelight.png
- trough-vertical-active.png
- trough-vertical.png
convert /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/slider-vert.png -resize 200% /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/slider-vert.png
convert /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/slider-vert-active.png -resize 200% /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/slider-vert-active.png
convert /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/slider-vert-insens.png -resize 200% /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/slider-vert-insens.png
convert /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/slider-vert-prelight.png -resize 200% /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/slider-vert-prelight.png
convert /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/trough-vertical-active.png -resize 200% /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/trough-vertical-active.png
convert /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/trough-vertical.png -resize 200% /usr/share/themes/Mint-Y-Dark/gtk-2.0/assets/trough-vertical.png
Cinnamon Theme
Unfortunately there are also lots of .svg files in /usr/share/themes/Mint-Y-Dark/cinnamon/ (both in subdirectories of /common-assets/ and /dark-assets/) with colors also hard-coded into them (bizarre, to say the least). These cannot be handled with ImageMagic convert, but rather either need to go through a process of conversion, grascaling, then converting back into .svg format (such as with Autotrace), or some other tool which can directly deal with color inside .svg files.
Edit the /usr/share/themes/Mint-Y-Dark/cinnamon/cinnamon.css file for color and scrollbar width. Replace #8fa876 with #993333 for a nice red to go with Mint-X-Red Icons.
Atom Application Scrollbars
Atom does not inherit these gtk configuration/theme settings and needs its Atom Scrollbars to be Configured Manually. Same with Visual Studio Code, scrollbars need to be set manually.
Screenshot default folder location
Screenshot default folder location needs to be set manually, such as:
gsettings set org.gnome.gnome-screenshot auto-save-directory ~/async-images-2019