Sable merle color-headed white
...
Then they also call the patterns of blue merle different names such as harlequin, etc....but that's all within the blue merle category.
Bless you for remembering sable merle-headed whites! Abigail was holding her breath. One small comment on the next statement, though. Sable merle can also be different names (like harlequin). I would consider Abbie a harlequin (or maybe a domino... there are too few pictures to compare to and I try not to claim to be an expert!).
Questions for our resident experts - can a sable merle (or sable merle-headed white) be a mahogany sable merle (or mahogany sable merle-headed white)?
Both sides of Abbie:
http://i800.photobucket.com/albums/yy282/the_gallows/Sheltie Gathering 2010/P7030050.jpg
http://s800.photobucket.com/albums/yy282/the_gallows/Sheltie Gathering 2010/P7030032.jpg
Lastly, what 'category' of sable would Duncan be? Sometimes he is so red or orange. His adult fur isn't done, but it has started.
http://s800.photobucket.com/albums/yy282/the_gallows/Sheltie Gathering 2010/P7030056.jpg

