My HSB Sliders aren't working - they're stuck in some weird default color positions that don't give me the preview of the color i'm sliding over - however the preview box does change. The slider just doesn't show the actual color range. 
Believe I seen a post not this before as a problem with CC2014. What version and OS are you on, check to see if there is a software update, and reset your prefs.
Jambottom,
It seems that the issue is caused by a corrupt folder called en_US or similar (depending on language) within the Adobe Illustrator 18 Settings folder, see post #7 by Jules in this thread,
https://forums.adobe.com/thread/1595766
so the solution should be to move or rename that folder (or the whole Adobe Illustrator 18 Settings folder).
You can find the folder in Move the folder (follow the link with that name) with Illy closed.
As a temporary roundabout way, you can select the lower rectangle to the right of the rainbow and DoubleClick to apply that to change the top rectangle and the values: the lower colour is the right one.
Unfortunately none of this has worked to solve the problem...