Adjust 2 default theme colors in ItemList and Tree

- Change Tree's drop_position_color from orange to white.
- Change ItemList's guide_color to the same color as Tree's, which fits in with a dark theme better.

doc/classes/ItemList.xml

@@ -445,7 +445,7 @@
 		<theme_item name="font_selected_color" data_type="color" type="Color" default="Color(1, 1, 1, 1)">
 			Text [Color] used when the item is selected.
 		</theme_item>
-		<theme_item name="guide_color" data_type="color" type="Color" default="Color(0, 0, 0, 0.1)">
+		<theme_item name="guide_color" data_type="color" type="Color" default="Color(0.7, 0.7, 0.7, 0.25)">
 			[Color] of the guideline. The guideline is a line drawn between each row of items.
 		</theme_item>
 		<theme_item name="h_separation" data_type="constant" type="int" default="4">

doc/classes/Tree.xml

@@ -461,7 +461,7 @@
 		<theme_item name="custom_button_font_highlight" data_type="color" type="Color" default="Color(0.95, 0.95, 0.95, 1)">
 			Text [Color] for a [constant TreeItem.CELL_MODE_CUSTOM] mode cell when it's hovered.
 		</theme_item>
-		<theme_item name="drop_position_color" data_type="color" type="Color" default="Color(1, 0.3, 0.2, 1)">
+		<theme_item name="drop_position_color" data_type="color" type="Color" default="Color(1, 1, 1, 1)">
 			[Color] used to draw possible drop locations. See [enum DropModeFlags] constants for further description of drop locations.
 		</theme_item>
 		<theme_item name="font_color" data_type="color" type="Color" default="Color(0.7, 0.7, 0.7, 1)">

scene/resources/default_theme/default_theme.cpp

@@ -741,7 +741,7 @@ void fill_default_theme(Ref<Theme> &theme, const Ref<Font> &default_font, const
 	theme->set_color("font_selected_color", "Tree", control_font_pressed_color);
 	theme->set_color("font_outline_color", "Tree", Color(1, 1, 1));
 	theme->set_color("guide_color", "Tree", Color(0.7, 0.7, 0.7, 0.25));
-	theme->set_color("drop_position_color", "Tree", Color(1, 0.3, 0.2));
+	theme->set_color("drop_position_color", "Tree", Color(1, 1, 1));
 	theme->set_color("relationship_line_color", "Tree", Color(0.27, 0.27, 0.27));
 	theme->set_color("parent_hl_line_color", "Tree", Color(0.27, 0.27, 0.27));
 	theme->set_color("children_hl_line_color", "Tree", Color(0.27, 0.27, 0.27));
@@ -776,7 +776,7 @@ void fill_default_theme(Ref<Theme> &theme, const Ref<Font> &default_font, const
 	theme->set_color("font_color", "ItemList", control_font_lower_color);
 	theme->set_color("font_selected_color", "ItemList", control_font_pressed_color);
 	theme->set_color("font_outline_color", "ItemList", Color(1, 1, 1));
-	theme->set_color("guide_color", "ItemList", Color(0, 0, 0, 0.1));
+	theme->set_color("guide_color", "ItemList", Color(0.7, 0.7, 0.7, 0.25));
 	theme->set_stylebox("selected", "ItemList", make_flat_stylebox(style_selected_color));
 	theme->set_stylebox("selected_focus", "ItemList", make_flat_stylebox(style_selected_color));
 	theme->set_stylebox("cursor", "ItemList", focus);