Setting the corner color in rotated PIL images

[rzed]

I'm using PIL to generate some images which may be rotated at the 
user's option. When they are rotated, the original image is cropped 
in the new image (which is fine), and the corners are black (which 
is not, in this case). I can't find any documented way to change 
the default fill color (if that's what it is) for the corners, and 
PIL also doesn't seem to support a flood fill. I have created a 
flood fill in Python, which works but which markedly slows image 
generation. 

Can anyone suggest a better way to set the color of the corners? 

All I really need in this case is that they be a solid color, the 
same color they were before being rotated. 

-- 
rzed