Can't handle float colors

[AstraLuma]

If colors are given as a float, things crash:

Traceback (most recent call last):
  File "viztests/text.py", line 29, in <module>
    ppb.run(starting_scene=TextScene)
  File "/home/astraluma/src/ppb/pursuedpybear/ppb/__init__.py", line 73, in run
    eng.run()
  File "/home/astraluma/src/ppb/pursuedpybear/ppb/engine.py", line 142, in run
    self.main_loop()
  File "/home/astraluma/src/ppb/pursuedpybear/ppb/engine.py", line 167, in main_loop
    self.loop_once()
  File "/home/astraluma/src/ppb/pursuedpybear/ppb/engine.py", line 183, in loop_once
    self.publish()
  File "/home/astraluma/src/ppb/pursuedpybear/ppb/engine.py", line 232, in publish
    method(event, self.signal)
  File "/home/astraluma/src/ppb/pursuedpybear/ppb/systems/renderer.py", line 166, in on_render
    self.render_background(render_event.scene)
  File "/home/astraluma/src/ppb/pursuedpybear/ppb/systems/renderer.py", line 185, in render_background
    sdl_call(
  File "/home/astraluma/src/ppb/pursuedpybear/ppb/systems/_sdl_utils.py", line 51, in sdl_call
    rv = func(*pargs, **kwargs)
ctypes.ArgumentError: argument 2: <class 'TypeError'>: wrong type