Add nicer dark and light colour sets (themes) used on terminals with 256

or more colours. Currently based these on emacs but they could change.
Terminals with fewer colours use the ANSI colours. A new "theme" option
overrides the detected theme (set to "terminal" to go back to ANSI
colours).

colour.c

@@ -26,6 +26,85 @@
 
 #include "tmux.h"
 
+/* Theme colour slots and their server options. */
+static const struct {
+	const char	*name;
+	const char	*dark_option;
+	const char	*light_option;
+	int		 terminal_colour;
+} colour_theme_table[] = {
+	{ "themeblack",
+	  "dark-theme-black",
+	  "light-theme-black",
+	  0
+	},
+	{ "themewhite",
+	  "dark-theme-white",
+	  "light-theme-white",
+	  7
+	},
+	{ "themelightgrey",
+	  "dark-theme-light-grey",
+	  "light-theme-light-grey",
+	  7
+	},
+	{ "themedarkgrey",
+	  "dark-theme-dark-grey",
+	  "light-theme-dark-grey",
+	  0
+	},
+	{ "themegreen",
+	  "dark-theme-green",
+	  "light-theme-green",
+	  2
+	},
+	{ "themeyellow",
+	  "dark-theme-yellow",
+	  "light-theme-yellow",
+	  3
+	},
+	{ "themered",
+	  "dark-theme-red",
+	  "light-theme-red",
+	  1
+	},
+	{ "themeblue",
+	  "dark-theme-blue",
+	  "light-theme-blue",
+	  4
+	},
+	{ "themecyan",
+	  "dark-theme-cyan",
+	  "light-theme-cyan",
+	  6
+	},
+	{ "thememagenta",
+	  "dark-theme-magenta",
+	  "light-theme-magenta",
+	  5
+	}
+};
+
+/* Get theme colour option. */
+const char *
+colour_theme_option(u_int n, enum client_theme theme)
+{
+	if (n >= nitems(colour_theme_table))
+		return (NULL);
+	if (theme == THEME_LIGHT)
+		return (colour_theme_table[n].light_option);
+	return (colour_theme_table[n].dark_option);
+}
+
+/* Get theme terminal colour. */
+int
+colour_theme_terminal_colour(u_int n)
+{
+	if (n >= nitems(colour_theme_table))
+		return (8);
+	return (colour_theme_table[n].terminal_colour);
+}
+
 static int
 colour_dist_sq(int R, int G, int B, int r, int g, int b)
 {
@@ -126,7 +205,7 @@ colour_dim(int c, u_int dim)
 {
 	u_char	r, g, b;
 
-	if (dim == 0 || COLOUR_DEFAULT(c))
+	if (dim == 0 || COLOUR_DEFAULT(c) || (c & COLOUR_FLAG_THEME))
 		return (c);
 	if (dim >= 100)
 		return (colour_join_rgb(0, 0, 0));
@@ -152,6 +231,13 @@ colour_tostring(int c)
 	if (c == -1)
 		return ("none");
 
+	if (c & COLOUR_FLAG_THEME) {
+		c &= 0xff;
+		if (c >= 0 && (u_int)c < nitems(colour_theme_table))
+			return (colour_theme_table[c].name);
+		return ("invalid");
+	}
+
 	if (c & COLOUR_FLAG_RGB) {
 		colour_split_rgb(c, &r, &g, &b);
 		xsnprintf(s, sizeof s, "#%02x%02x%02x", r, g, b);
@@ -252,6 +338,7 @@ colour_fromstring(const char *s)
 	const char	*cp;
 	int		 n;
 	u_char		 r, g, b;
+	u_int		 i;
 
 	if (*s == '#' && strlen(s) == 7) {
 		for (cp = s + 1; isxdigit((u_char) *cp); cp++)
@@ -282,6 +369,11 @@ colour_fromstring(const char *s)
 	if (strcasecmp(s, "terminal") == 0)
 		return (9);
 
+	for (i = 0; i < nitems(colour_theme_table); i++) {
+		if (strcasecmp(s, colour_theme_table[i].name) == 0)
+			return (i|COLOUR_FLAG_THEME);
+	}
+
 	if (strcasecmp(s, "black") == 0 || strcmp(s, "0") == 0)
 		return (0);
 	if (strcasecmp(s, "red") == 0 || strcmp(s, "1") == 0)