Strange....
Most black dyes have blue in them, and sometimes other colors too. I suspect since it is a dry clean only... that water and perhaps in this case perspiration dissolved some of the dye.
Here is a short site explaining that rayon does deteriorate.
http://www.redrockthreads.com/rayonthread/
I'd say the dress is "toast" and toss it.
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All truths are easy to understand once they are discovered; the point is to discover them.-- Galileo Galilei
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Weezie looking at petunias 8.25.2017
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