Turn on greyscale button?

Does anybody know how to make it so when you click on a GUI a player's view turns to greyscale?

What you could do is have a localscript that detects when the GUI button is pressed and then you can insert the ColorCorrection effect. Setting the saturation to a negative value makes it look grayscale.

Here's what the localscript might look like:

local guiButton = script.Parent
guiButton.MouseButton1Click:Connect(function()
	local effect = Instance.New("ColorCorrectionEffect")
	effect.Saturation = -1
	effect.Parent = game:GetService("Lighting")
end)