I'm on a mac and the ctrl isn't doing... anything. I can set up a key to activate the color picker but it only switches, not works as a sticky key for me to quickly color select while blending.

Any advice would be very welcome!

I am using Krita on Mac, too. The color picker works for me. When it says the sticky key is set to 'ctrl', it is actually the 'cmd' key on your keyboard. If you want to redirect the key to the actual 'ctrl' on your keyboard, go to 'preferences'->'canvas input settings'->'alternate invocation', and when you press the 'ctrl' key, you will notice it says 'meta'. In Mac terms, 'meta' means the options key, but just ignore what it says and use 'ctrl' - it will work.