Theme chance to create the theme and Yaru icon in the colors of Ubuntu-Mate? In the gnome-look has the Communitheme-Gray compatible for the Mate.
It seems pretty easy if you are adept with GIMP and use its channel mixer to change up the icon colours. You should be able to mix down into a pleasing shade of pale olive-lime green.
Figured I would forward this cool trick; make symbolic links of everything within Caja, in a new directory except for the theme configuration file so you can have the same exact theme using the same files from their original paths under a different name. Then as you replace links with actual files, you will see it change over time while using the base theme, so you can re-use assets without wasting space on duplicate files.
As Caja doesn’t produce links with the same name, rather renaming them Link to
x
, you can install gprename
to batch-rename and remove the preceding text.