HexEditor: Gray-out null bytes

This should improve an overall visibility of "meaningful" data. :^)

Userland/Applications/HexEditor/HexEditor.cpp

@@ -604,8 +604,17 @@ void HexEditor::paint_event(GUI::PaintEvent& event)
                 line_height() - m_line_spacing
             };
 
+            const u8 cell_value = m_document->get(byte_position).value;
+            auto line = String::formatted("{:02X}", cell_value);
+
             Gfx::Color background_color = palette().color(background_role());
-            Gfx::Color text_color = edited_flag ? Color::Red : palette().color(foreground_role());
+            Gfx::Color text_color = [&]() -> Gfx::Color {
+                if (edited_flag)
+                    return Color::Red;
+                if (cell_value == 0x00)
+                    return palette().color(ColorRole::PlaceholderText);
+                return palette().color(foreground_role());
+            }();
 
             if (highlight_flag) {
                 background_color = edited_flag ? palette().selection().inverted() : palette().selection();
@@ -616,8 +625,6 @@ void HexEditor::paint_event(GUI::PaintEvent& event)
             }
             painter.fill_rect(hex_display_rect, background_color);
 
-            const u8 cell_value = m_document->get(byte_position).value;
-            auto line = String::formatted("{:02X}", cell_value);
             painter.draw_text(hex_display_rect, line, Gfx::TextAlignment::TopLeft, text_color);
 
             if (m_edit_mode == EditMode::Hex) {
@@ -640,7 +647,13 @@ void HexEditor::paint_event(GUI::PaintEvent& event)
             };
 
             background_color = palette().color(background_role());
-            text_color = edited_flag ? Color::Red : palette().color(foreground_role());
+            text_color = [&]() -> Gfx::Color {
+                if (edited_flag)
+                    return Color::Red;
+                if (cell_value == 0x00)
+                    return palette().color(ColorRole::PlaceholderText);
+                return palette().color(foreground_role());
+            }();
 
             if (highlight_flag) {
                 background_color = edited_flag ? palette().selection().inverted() : palette().selection();