Expand colours as formats like styles.

style.c

@@ -434,6 +434,29 @@ style_apply(struct grid_cell *gc, struct options *oo, const char *name,
 	style_add(gc, oo, name, ft);
 }
 
+/* Parse a single colour into a style */
+int
+style_parse_colour(struct style *sy, const struct grid_cell *base,
+    const char *s)
+{
+	int	c;
+
+	style_set(sy, base);
+
+	if (*s == '\0') {
+		sy->gc.fg = -1;
+		return (0);
+	}
+
+	if ((c = colour_fromstring(s)) == -1)
+		return (-1);
+	if (c == 8)
+		sy->gc.fg = base->fg;
+	else
+		sy->gc.fg = c;
+	return (0);
+}
+
 /* Initialize style from cell. */
 void
 style_set(struct style *sy, const struct grid_cell *gc)