Make terminal true-colour mode configurable.

I know some users don't like any colour _at all_, and we have a
separate option to turn off xterm-style 256-colour sequences, so it
seems remiss not to have an option to disable true colour as well.

config.c

@@ -1898,6 +1898,9 @@ void setup_config_box(struct controlbox *b, int midsession,
     ctrl_checkbox(s, "Allow terminal to use xterm 256-colour mode", '2',
 		  HELPCTX(colours_xterm256), conf_checkbox_handler,
 		  I(CONF_xterm_256_colour));
+    ctrl_checkbox(s, "Allow terminal to use 24-bit colours", '4',
+		  HELPCTX(colours_truecolour), conf_checkbox_handler,
+		  I(CONF_true_colour));
     ctrl_radiobuttons(s, "Indicate bolded text by changing:", 'b', 3,
                       HELPCTX(colours_bold),
                       conf_radiobutton_handler, I(CONF_bold_style),

doc/config.but

@@ -1549,6 +1549,15 @@ If you do not see \cq{colors#256} in the output, you may need to
 change your terminal setting. On modern Linux machines, you could
 try \cq{xterm-256color}.
 
+\S{config-truecolour} \q{Allow terminal to use 24-bit colour}
+
+\cfg{winhelp-topic}{colours.truecolour}
+
+This option is enabled by default. If it is disabled, PuTTY will
+ignore any control sequences sent by the server which use the control
+sequences supported by modern terminals to specify arbitrary 24-bit
+RGB colour value.
+
 \S{config-boldcolour} \q{Indicate bolded text by changing...}
 
 \cfg{winhelp-topic}{colours.bold}

putty.h

@@ -859,6 +859,7 @@ void cleanup_exit(int);
     /* Colour options */ \
     X(INT, NONE, ansi_colour) \
     X(INT, NONE, xterm_256_colour) \
+    X(INT, NONE, true_colour) \
     X(INT, NONE, system_colour) \
     X(INT, NONE, try_palette) \
     X(INT, NONE, bold_style) \

settings.c

@@ -609,6 +609,7 @@ void save_open_settings(void *sesskey, Conf *conf)
     write_setting_i(sesskey, "TryPalette", conf_get_int(conf, CONF_try_palette));
     write_setting_i(sesskey, "ANSIColour", conf_get_int(conf, CONF_ansi_colour));
     write_setting_i(sesskey, "Xterm256Colour", conf_get_int(conf, CONF_xterm_256_colour));
+    write_setting_i(sesskey, "TrueColour", conf_get_int(conf, CONF_true_colour));
     write_setting_i(sesskey, "BoldAsColour", conf_get_int(conf, CONF_bold_style)-1);
 
     for (i = 0; i < 22; i++) {
@@ -1005,6 +1006,7 @@ void load_open_settings(void *sesskey, Conf *conf)
     gppi(sesskey, "TryPalette", 0, conf, CONF_try_palette);
     gppi(sesskey, "ANSIColour", 1, conf, CONF_ansi_colour);
     gppi(sesskey, "Xterm256Colour", 1, conf, CONF_xterm_256_colour);
+    gppi(sesskey, "TrueColour", 1, conf, CONF_true_colour);
     i = gppi_raw(sesskey, "BoldAsColour", 1); conf_set_int(conf, CONF_bold_style, i+1);
 
     for (i = 0; i < 22; i++) {

terminal.c

@@ -1458,6 +1458,7 @@ void term_copy_stuff_from_conf(Terminal *term)
     term->scroll_on_disp = conf_get_int(term->conf, CONF_scroll_on_disp);
     term->scroll_on_key = conf_get_int(term->conf, CONF_scroll_on_key);
     term->xterm_256_colour = conf_get_int(term->conf, CONF_xterm_256_colour);
+    term->true_colour = conf_get_int(term->conf, CONF_true_colour);
 
     /*
      * Parse the control-character escapes in the configured
@@ -5171,7 +5172,6 @@ static void do_paint(Terminal *term, Context ctx, int may_optimise)
                 tattr = (tattr & ~(ATTR_FGMASK | ATTR_BGMASK)) | 
                 ATTR_DEFFG | ATTR_DEFBG;
 
-	    tc = d->truecolour;
 	    if (!term->xterm_256_colour) {
 		int colour;
 		colour = (tattr & ATTR_FGMASK) >> ATTR_FGSHIFT;
@@ -5182,6 +5182,12 @@ static void do_paint(Terminal *term, Context ctx, int may_optimise)
 		    tattr = (tattr &~ ATTR_BGMASK) | ATTR_DEFBG;
 	    }
 
+            if (term->true_colour) {
+                tc = d->truecolour;
+            } else {
+                tc.fg = tc.bg = optionalrgb_none;
+            }
+
 	    switch (tchar & CSET_MASK) {
 	      case CSET_ASCII:
 		tchar = term->ucsdata->unitab_line[tchar & 0xFF];

terminal.h

@@ -325,6 +325,7 @@ struct terminal_tag {
     int scroll_on_disp;
     int scroll_on_key;
     int xterm_256_colour;
+    int true_colour;
 };
 
 #define in_utf(term) ((term)->utf || (term)->ucsdata->line_codepage==CP_UTF8)

windows/winhelp.h

@@ -125,6 +125,7 @@
 #define WINHELP_CTX_selection_rtf "selection.rtf:config-rtfpaste"
 #define WINHELP_CTX_colours_ansi "colours.ansi:config-ansicolour"
 #define WINHELP_CTX_colours_xterm256 "colours.xterm256:config-xtermcolour"
+#define WINHELP_CTX_colours_truecolour "colours.truecolour:config-truecolour"
 #define WINHELP_CTX_colours_bold "colours.bold:config-boldcolour"
 #define WINHELP_CTX_colours_system "colours.system:config-syscolour"
 #define WINHELP_CTX_colours_logpal "colours.logpal:config-logpalette"