I did a preemptive spraying for spider mites when Hoya ischnopus was in bloom, and two days later the flowers turned this interesting caramel color.  I am unsure if it is related, or if the blooms would have turned this color of their own accord.  I am going to have to guess at this point that it is related.  Here is the final photo of Hoya ischnopus for the year:

Hoya ischnopus After Spraying with Azamax – Summer 2014