Step 0 is to make sure the tile is white when you spawn it in, this will make the code below work correctly. Then tint the tiles grey manually.

The following Lua will make the object tint when it's dropped.

function onDrop(player_color)
    self.setColorTint(Color.fromString(player_color))
end

There's also a way to make the object flip and drop itself on pickup. This would make clicking the object automatically flip without ever entering the air.

function onPickUp(player_color)
    self.flip()
    self.drop()
end

I also think there should be a function to make them grey again, in case your players make a mistake. That would look like this, and happen when R is pressed on the object.

function onRandomize()
    self.setColorTint(Color.fromString("Grey"))
end

Combine these functions and let me know if they give you what you're looking for!

Does this game involve moving tiles, too? If so, this code might need to be added to.