...Colors are not enabled by default in macOS Terminal, so you will need to enable colors in order for this theme to work. For One Dark, use the same color for "Black" as that used for the window background (#1E2127). Using a brighter text color for the One Dark theme and remove transparency from backgrounds. Using generic RGB for colors; 95% opaque backgrounds. Alternate theme using a darker window color, based on the outer ui and not the editor space.