Pictured below is a blue merle catahoula. Australian Cattle Dogs (ACD or Blue Heeler) are not Merle.  Merle color pattern is distinguished by the presence of irregular dark blotches against a lighter background of the same general basic pigment. Merle     This coloring is "due to a dominant color pattern factor" and is seen in breeds such as the Cardigan Corgi, Australian Shepard and Catahoula.   "The use of "merle" in name of the ACD ancestor, the Northumberland Blue Merle Drovers Dog, was 18th and 19th century useage of the word, and used to describe "marbled" or "mottled" coat color.  Just a very general color term with no genetic implications at all."  Noreen Clark

The blue ACD is blue-mottled or blue speckled with or without other markings and a red ACD should be an even red speckle all over with or without darker red markings on the head.

This ACD is a dark "blue" speckle

  This blue dog shows the most common  "ticking" or salt and pepper speckling of the ACD with face patches and tan markings. This is not correctly called a tri . 

This dog shows the larger speckling

This is an example of  red speckle and red with face markings Eyes are brown and noses are black for both colors.

Please go to Noreen Clark's informative site:
*** A DOG CALLED BLUE ***
 Australian Cattle Dog pedigrees & historical resources
                 http://www.adcb.au.com