Alpha channel transparency value consistency

[Daniel J S. <dan...@ie...>]

I'm working on something with alpha channel and noticed that the alpha 
channel 0 to 1 range behaves differently for color specification and for 
input data.  For color spec (help colorspec):

  "#AARRGGBB" represents an RGB color with an alpha channel (transparency)
  value in the high bits. An alpha value of 0 represents a fully opaque 
color;
  i.e., "#00RRGGBB" is the same as "#RRGGBB".

and for rgbalpha (help alpha):

  The `rgbalpha` plotting style assumes that each pixel of input data 
contains
  an alpha value in the range [0:255].  A pixel with alpha = 0 is purely
  transparent and does not alter the underlying contents of the plot. A 
pixel
  with alpha = 255 is purely opaque.

Was there a reason for the opposite correlation of the opacity/transparency?

Dan