Actually the difference is in more than just color. Though the status of the Brooks has changed, there are differnces between it and what is called a Florida King. The problem has a great deal to do with the canal system that opened the Brook's dwindling range to snakes that are IMO intergrades. In recent years the Brook's king has become established as the same thing as a Florida king. The thing is that there is a wide zone of integration between them and the Northern chain. This intergradiation is now practically complete in wild populations except for the remaing Brooks that are in extreme south Dade and Monroe counties.
I should point out I have lived in S. Florida since 1957 and actively collected kings in the field till 1985.
Brooks/S. Florida kings (besides yellow color) are distinct in that usually the head is blunter than a "Florida intergrade". Early descriptions mentioned the lack of a Loreal scale (found between the eye and nose). Also Brooks are charactorised by the large amount of dark banding (over 78. I have seen some with over 100)which aids in the illusion of patternlessness in the best examples.
There is also a Black/white phase found near Turkey Point which are the ancestors of the popular color phase.
Frank
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"The luxury of not getting involved departed with the last lifeboat Skipper..."