code: def set_source_rgba(self, red, green, blue, alpha=1):
          
          cairo.cairo_set_source_rgba(self._pointer, red, green, blue, alpha)
          self._check_status()
docs: Sets the source pattern within this context to a solid color.
          This color will then be used for any subsequent drawing operation
          until a new source pattern is set.
  
          The color and alpha components are
          floating point numbers  in the range 0 to 1.
          If the values passed in are outside that range, they will be clamped.
  
          The default source pattern is opaque black,
          (that is, it is equivalent to ``context.set_source_rgba(0, 0, 0)``).
  
          :param red: Red component of the color.
          :param green: Green component of the color.
          :param blue: Blue component of the color.
          :param alpha:
              Alpha component of the color.
              1 (the default) is opaque, 0 fully transparent.
          :type red: float
          :type green: float
          :type blue: float
          :type alpha: float