Assuming backslashes themselves could be escaped, you want to split on colons which are preceeded by an even amount of backslashes. You can't do look behind in this case, because you can't do variable length look behind.

But you can reverse the string, and look for an even amount of trailing backslashes. After splitting, you need to do some reversing again:

reverse map {scalar reverse} split /:(?=(?:\\\\)*(?!\\))/ => reverse $
+string;
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Abigail