Change default background color to black

While the pink background color is useful for debugging, Catacomb has
long outlived its experimental stage and a black background color is a
little less jarring during startup.

src/udev.rs

@@ -57,7 +57,7 @@ use crate::trace_error;
 use crate::windows::Windows;
 
 /// Default background color.
-const CLEAR_COLOR: [f32; 4] = [1., 0., 1., 1.];
+const CLEAR_COLOR: [f32; 4] = [0., 0., 0., 1.];
 
 /// Time before a VBlank reserved for rendering compositor updates.
 const RENDER_TIME_OFFSET: Duration = Duration::from_millis(10);