Make color0 distinct from background/foreground and fix helix theme (#5538)

* Make color0 distinct from background/foreground

The majority of themes have color0 available as a subtle offset from
the background. For flexoki-light, because color0 matched foreground, it
wasn't subtle, and would cause invisible text when used as a background
color (e.g., in text editor rulers). For vantablack, ethereal,
hackerman, and white, color0 matched background and would cause
invisible text when a theme wanted text to be de-emphasized.

This patch makes it consistently a subtle offset from background.

* Make helix selection theme colors more subtle

Helix is more usable if the selection background is subtle. This is
primarily because of [[1]], which makes a bright selection like we had
before often make the foreground text unreadable in the picker preview.

[1]: https://github.com/helix-editor/helix/issues/12405

themes/ethereal/colors.toml

@@ -5,7 +5,7 @@ background = "#060B1E"
 selection_foreground = "#060B1E"
 selection_background = "#ffcead"
 
-color0 = "#060B1E"
+color0 = "#3C486D"
 color1 = "#ED5B5A"
 color2 = "#92a593"
 color3 = "#E9BB4F"

themes/flexoki-light/colors.toml

@@ -5,7 +5,7 @@ background = "#FFFCF0"
 selection_foreground = "#100F0F"
 selection_background = "#CECDC3"
 
-color0 = "#100F0F"
+color0 = "#DAD8CE"
 color1 = "#D14D41"
 color2 = "#879A39"
 color3 = "#D0A215"

themes/hackerman/colors.toml

@@ -5,7 +5,7 @@ background = "#0B0C16"
 selection_foreground = "#0B0C16"
 selection_background = "#ddf7ff"
 
-color0 = "#0B0C16"
+color0 = "#3E4058"
 color1 = "#50f872"
 color2 = "#4fe88f"
 color3 = "#50f7d4"

themes/vantablack/colors.toml

@@ -11,7 +11,7 @@ selection_foreground = "#000000"
 selection_background = "#ffffff"
 
 # Normal colors (ANSI 0-7)
-color0 = "#000000"
+color0 = "#404040"
 color1 = "#a4a4a4"
 color2 = "#b6b6b6"
 color3 = "#cecece"

themes/white/colors.toml

@@ -11,7 +11,7 @@ selection_foreground = "#ffffff"
 selection_background = "#1a1a1a"
 
 # Normal colors (ANSI 0-7)
-color0 = "#ffffff"
+color0 = "#c0c0c0"
 color1 = "#2a2a2a"
 color2 = "#3a3a3a"
 color3 = "#4a4a4a"