Refer to the circled part in the image.
It's a spectrum that shows up as part of the color window. The only options I see are to switch it to a different type of spectrum, such as Grayscale, CMYK, etc. But there's no option to completely get rid of it while still using the color sliders. I don't remember having this problem with earlier versions of PS, so it must have come with an update.
If there is a way to disable it, please let me know. Or perhaps someone can write me a mod or something. Because it's annoying how much space this takes up. I realize I can minimize it to only a thin bar, but I have to do that every time I switch to fullscreen mode, and I really wish I didn't.
I used cs6 before this. I didn't hide the spectrum, but I don't remember it ever expanding like it does in CC.