Moved to the correct forum (i hope).
I use OSX El Capitan Version 10.11.14, and I experienced the same problem with my Flash CS5.5.
I found that you can get around this problem if you are working with your own graphics. Keep double clicking on the movie clip/graphic/object/group with the colour that you want to copy, until you find the source Shape that contains that colour.
On the Properties window, you should see the Fill and Stroke of that Shape. The Fill property of the shape should be the colour you want to copy. If you save your file (Ctrl-S), you should notice that the Foreground Colour in the Toolbox changes into the Fill colour of the selected shape.
Hope this works for you!