Same problem with Photoshop CC2014
thanks for the response. we can't be the only ones.
I noticed that I'm able to use the Adobe color picker but its not my favorite way to go.
I have this issue too, with Yosemite and PSCC2014 on my new iMac 27" non-retina.
As jL2000 says, the Adobe color picker works, but it never was as good as the Apple one.
The little magnifying glass that seems to have vanished from Yosemite was always preferable to Adobe's equivalent as a sampling tool.
I guess we need to lobby Adobe to up the performance of their tool, as Apple doesn't tend to listen to user feedback. To me, this is a real loss in PS performance