diff --git a/engines/glk/frotz/config.h b/engines/glk/frotz/config.h
index 709999647471..80dd6ebf2c42 100644
--- a/engines/glk/frotz/config.h
+++ b/engines/glk/frotz/config.h
@@ -148,8 +148,8 @@ struct UserOptions {
 	int _undo_slots;
 	int _script_cols;
 	int _err_report_mode;
-	int _defaultForeground;
-	int _defaultBackground;
+	uint _defaultForeground;
+	uint _defaultBackground;
 	bool _color_enabled;
 
 	/**
diff --git a/engines/glk/frotz/glk_interface.cpp b/engines/glk/frotz/glk_interface.cpp
index 28826d8d4e38..48203bf7e58f 100644
--- a/engines/glk/frotz/glk_interface.cpp
+++ b/engines/glk/frotz/glk_interface.cpp
@@ -160,13 +160,12 @@ void GlkInterface::initialize() {
 
 	// Set up the foreground & background
 	_color_enabled = ((h_version >= 5) && (h_flags & COLOUR_FLAG))
-			|| (_defaultForeground != -1) || (_defaultBackground != -1);
+			|| (_defaultForeground != zcolor_Transparent) || (_defaultBackground != zcolor_Transparent);
 
 	if (_color_enabled) {
 		h_config |= CONFIG_COLOUR;
 		h_flags |= COLOUR_FLAG;		// FIXME: beyond zork handling?
 
-		assert(_defaultForeground != -1 && _defaultBackground != -1);
 		h_default_foreground = BLACK_COLOUR;
 		h_default_background = WHITE_COLOUR;
 		zcolors[h_default_foreground] = _defaultForeground;