Let bw theme inherit overridden colors

- Mark derived color slots undefined so fg/bg/list-bg propagate
- Add missing Footer slot (was rendering black)

src/tui/tui.go

@@ -1003,50 +1003,55 @@ func init() {
 
 	NoColorTheme = &ColorTheme{
 		Colored: false,
+		// Root colors. Everything else is left undefined so that overriding a
+		// root (e.g. --color bw,bg:blue) propagates to the derived colors,
+		// just like in the colored base themes.
 		Input:       defaultColor,
 		Fg:          defaultColor,
 		Bg:          defaultColor,
-		ListFg:           defaultColor,
-		ListBg:           defaultColor,
-		AltBg:            undefined,
-		SelectedFg:       defaultColor,
-		SelectedBg:       defaultColor,
-		SelectedMatch:    defaultColor,
 		DarkBg:      defaultColor,
 		Prompt:      defaultColor,
 		Match:       defaultColor,
-		Current:          undefined,
-		CurrentMatch:     undefined,
 		Spinner:     defaultColor,
 		Info:        defaultColor,
 		Pointer:     defaultColor,
 		Marker:      defaultColor,
 		Header:      defaultColor,
-		Border:           undefined,
+		Footer:      defaultColor,
 		BorderLabel: defaultColor,
+		// Derived colors. Left undefined so they inherit from a root.
+		ListFg:           undefined,
+		ListBg:           undefined,
+		AltBg:            undefined,
+		SelectedFg:       undefined,
+		SelectedBg:       undefined,
+		SelectedMatch:    undefined,
+		Current:          undefined,
+		CurrentMatch:     undefined,
+		Border:           undefined,
 		Ghost:            undefined,
-		Disabled:         defaultColor,
+		Disabled:         undefined,
-		PreviewFg:        defaultColor,
+		PreviewFg:        undefined,
-		PreviewBg:        defaultColor,
+		PreviewBg:        undefined,
 		Gutter:           undefined,
 		AltGutter:        undefined,
-		PreviewBorder:    defaultColor,
+		PreviewBorder:    undefined,
-		PreviewScrollbar: defaultColor,
+		PreviewScrollbar: undefined,
-		PreviewLabel:     defaultColor,
+		PreviewLabel:     undefined,
-		ListLabel:        defaultColor,
+		ListLabel:        undefined,
-		ListBorder:       defaultColor,
+		ListBorder:       undefined,
-		Separator:        defaultColor,
+		Separator:        undefined,
-		Scrollbar:        defaultColor,
+		Scrollbar:        undefined,
-		InputBg:          defaultColor,
+		InputBg:          undefined,
-		InputBorder:      defaultColor,
+		InputBorder:      undefined,
-		InputLabel:       defaultColor,
+		InputLabel:       undefined,
-		HeaderBg:         defaultColor,
+		HeaderBg:         undefined,
-		HeaderBorder:     defaultColor,
+		HeaderBorder:     undefined,
-		HeaderLabel:      defaultColor,
+		HeaderLabel:      undefined,
-		FooterBg:         defaultColor,
+		FooterBg:         undefined,
-		FooterBorder:     defaultColor,
+		FooterBorder:     undefined,
-		FooterLabel:      defaultColor,
+		FooterLabel:      undefined,
-		GapLine:          defaultColor,
+		GapLine:          undefined,
 		Nth:              undefined,
 		Nomatch:          undefined,
 	}