Add setting for alternative linkgraph overlay colour schemes

src/table/settings.ini

@@ -52,6 +52,7 @@ static bool SimulatedWormholeSignalsChanged(int32 p1);
 static bool EnableSingleVehSharedOrderGuiChanged(int32 p1);
 static bool CheckYapfRailSignalPenalties(int32 p1);
 static bool ViewportMapShowTunnelModeChanged(int32 p1);
+static bool UpdateLinkgraphColours(int32 p1);
 
 static bool UpdateClientName(int32 p1);
 static bool UpdateServerPassword(int32 p1);
@@ -4952,6 +4953,20 @@ strhelp  = STR_CONFIG_SETTING_SHOW_NEWGRF_NAME_HELPTEXT
 proc     = RedrawScreen
 cat      = SC_ADVANCED
 
+[SDTC_VAR]
+var      = gui.linkgraph_colours
+type     = SLE_UINT8
+flags    = SLF_NOT_IN_SAVE | SLF_NO_NETWORK_SYNC
+guiflags = SGF_MULTISTRING
+def      = 0
+min      = 0
+max      = 3
+str      = STR_CONFIG_SETTING_LINKGRAPH_COLOURS
+strhelp  = STR_CONFIG_SETTING_LINKGRAPH_COLOURS_HELPTEXT
+strval   = STR_CONFIG_SETTING_LINKGRAPH_COLOURS_GREEN_TO_RED
+proc     = UpdateLinkgraphColours
+cat      = SC_BASIC
+
 ; For the dedicated build we'll enable dates in logs by default.
 [SDTC_BOOL]
 ifdef    = DEDICATED