I tested KDE and saw that it changes the colors of the GTK Breeze theme using a file called colors.css that is in the $HOME/.config/gtk-3.0 folder.
The gtk-3.0 folders of the Snap apps have links to the files in the $HOME/.config/gtk-3.0 folder, but they do not have a link to the colors.css file that KDE creates.
This creates a huge visual inconsistency in the system, because while the native GTK apps follow the colors used by KDE, the GTK Snap apps continue to use the default Breeze colors.
Would it be possible to change this? Make the Snap apps start accessing the colors.css file in the $HOME/.config/gtk-3.0 folder