Swordfish:
A couple of thoughts. First, color is relative. There seems to be a general observation that in warm climates red does not develop as well as in 4 season climates, but Sumi does fine. Twenty years ago, however, there was much talk about the need for cool seasons to get Sumi to rise. The improvement of Sumi over the past 20 years seems to have had major benefits for koikeepers in warm climates.
Which leads to the second thought: the article is from 1994. There has been much genetic improvement of the Hi in koi over the past dozen years ... more stable, deeper, thicker. The observations in 1994 may have been accurate, but not as applicable to today's better quality koi.
Third: Water quality. My personal obsewrvation has been that koi raised in Florida do not have Hi as intense and even as koi raised in a 4 season climate, but the ones raised in optimal water conditions come closer to meeting the standard set by the 4 season koi. As we have learned more about water maintenance, and certainly much has been learned (and become available) over the past dozen years, the more likely the differences between warm climate Hi and 4 season Hi have narrowed.
Fourth: We should never take what is written in an article (or a koi board) as a fixed truth. Einstein showed that all the conventional wisdom can be wrong, even if it accurately predicts virtually all that occurs. And, like history, the perspective from which something is written should be weighed before accepting or rejecting the conclusions.
