Change the named color 'transparent' to transparent black

Include/RmlUi/Core/ComputedValues.h

@@ -107,7 +107,7 @@ namespace Style {
 		Colourb border_top_color{255, 255, 255}, border_right_color{255, 255, 255}, border_bottom_color{255, 255, 255},
 			border_left_color{255, 255, 255};
 
-		Colourb background_color = Colourb(255, 255, 255, 0);
+		Colourb background_color = Colourb(0, 0, 0, 0);
 	};
 
 	struct InheritedValues {

Source/Core/PropertyParserColour.cpp

@@ -51,7 +51,7 @@ PropertyParserColour::PropertyParserColour()
 	html_colours["blue"] =  Colourb(0, 0, 255);
 	html_colours["teal"] =  Colourb(0, 128, 128);
 	html_colours["aqua"] = Colourb(0, 255, 255);
-	html_colours["transparent"] = Colourb(255, 255, 255, 0);
+	html_colours["transparent"] = Colourb(0, 0, 0, 0);
 }
 
 PropertyParserColour::~PropertyParserColour()