It is possible, absolutely. :)
Rusty is an amazing dog and was unexpected, as you can read in his profile page here…
However, red merle is NOT in the allowed colors of the standard. They crop up when you have two dogs carrying the recessive “liver” color that dilutes the black on a dog to chocolate. Liver is “bb” - so the parents in Rusty’s case were each Bb and no one knew it. Rusty’s brother is “bb” (liver) and Rusty is “bb” (liver) with the merle gene splashed over it.
Now here’s a quick concerned disclaimer from me….
If someone tries to sell you a “rare red merle” in Cardigans… (and sadly I’ve seen it crop up on a few questionable websites…)
I’d have to say if they used the term “rare” and attempted to sell you it for more money — don’t do it. :) They’re rare because they’re not accepted in the standard as a color. No other reason.
When I see someone specifically breeding for red merles in Cardigans there’s some questionable practices going on. :(
Hope that answers your question!