Connect color button to start function

And fix show and hide behaviors.

HUD.gd

@@ -17,6 +17,7 @@ func show_game_over():
 	$MessageLabel.show()
 	yield(get_tree().create_timer(1.0), "timeout")
 	$StartButton.show()
+	$ColorButton.show()
 
 func update_score(score):
 	$ScoreLabel.text = str(score)
@@ -28,4 +29,5 @@ func _on_MessageTimer_timeout():
 
 func _on_StartButton_pressed():
 	$StartButton.hide()
+	$ColorButton.hide()
 	emit_signal("start_game")

HUD.tscn

@@ -97,3 +97,4 @@ expand = true
 stretch_mode = 4
 [connection signal="pressed" from="StartButton" to="." method="_on_StartButton_pressed"]
 [connection signal="timeout" from="MessageTimer" to="." method="_on_MessageTimer_timeout"]
+[connection signal="pressed" from="ColorButton" to="." method="_on_StartButton_pressed"]