def _transition_stage(self, step, total_steps,<EOL>brightness=None, color=None):
if brightness is not None:<EOL><INDENT>self._assert_is_brightness(brightness)<EOL>brightness = self._interpolate(self.brightness, brightness,<EOL>step, total_steps)<EOL><DEDENT>if color is not None:<EOL><INDENT>self._assert_is_color(color)<EOL>color = Color(*[self._interpolate(self.color[i], color[i],<EOL>step, total_steps)<EOL>for i in range(<NUM_LIT:3>)])<EOL><DEDENT>return {'<STR_LIT>': brightness, '<STR_LIT>': color}<EOL>
Get a transition stage at a specific step.

:param step: The current step.
:param total_steps: The total number of steps.
:param brightness: The brightness to transition to (0.0-1.0).
:param color: The color to transition to.
:return: The stage at the specific step.