BrickColour is not a valid member of UnionOperation?

I know that a Union has a BrickColour but for the script I'm using won't work and has the same error (BrickColour is not a valid member of UnionOperation) in the output.

The script:

-- Local Script
local player = game.Players.LocalPlayer
game.Workspace.BloodReader.NeedleStand.ClickDetector.MouseClick:Connect(function()
    game.Workspace.Event:FireServer(player)
    player.Backpack.Collector.MovingParts.Change.BrickColour = BrickColor.new("Fossil")
end)

If anyone knows how to fix this please help.