fullscreen_bg defaults to black

Per conversation at PR #1147 with @kilpilainen

README.md

@@ -75,7 +75,7 @@ seatd daemon.
 When dwl is run with no arguments, it will launch the server and begin handling
 any shortcuts configured in `config.h`. There is no status bar or other
 decoration initially; these are instead clients that can be run within the
-Wayland session. Do note that the default background color is black. This can be
+Wayland session. Do note that the default background color is grey. This can be
 modified in `config.h`.
 
 If you would like to run a script or command automatically at startup, you can

config.def.h

@@ -12,7 +12,7 @@ static const float bordercolor[]           = COLOR(0x444444ff);
 static const float focuscolor[]            = COLOR(0x005577ff);
 static const float urgentcolor[]           = COLOR(0xff0000ff);
 /* This conforms to the xdg-protocol. Set the alpha to zero to restore the old behavior */
-static const float fullscreen_bg[]         = {0.1f, 0.1f, 0.1f, 1.0f}; /* You can also use glsl colors */
+static const float fullscreen_bg[]         = {0.0f, 0.0f, 0.0f, 1.0f}; /* You can also use glsl colors */
 
 /* tagging - TAGCOUNT must be no greater than 31 */
 #define TAGCOUNT (9)