How to make it so that when a keycard touches the block it change color?

I want to know how you would change the color of a block. Lets say i touched a block once and the color is green but i want it to stay green and then when i touch it again with the keycard it turns red so far I can only get it to change one color.....

door = script.Parent
open = false

script.Parent.Touched:Connect(function(part)
    local keycard = part:FindFirstChild("keycard")
    if keycard ~= nil and keycard.value == true and then 
        open = true
        if open ~= true then
        script.Parent.color.brickcolor = BrickColor.new("Really Red")
        else
                script.Parent.color.brickcolor = BrickColor.new("Bright Green")
    end



end)