keep in the dark
To intentionally withhold information from someone. Either to avoid confrontation or to gain from the other’s lack of information. From the comparison to mushrooms, “I’m like a mushroom, then keep me in the dark and feed me bullshit.”
When it comes to keeping something secret, the plan should be to keep in the dark.
keeping dark
To hide or conceal something that might be incriminating to you.
I promised my wife that I would stop gambling, so I'm definitely keeping dark my recent loss at the race track!