Why does the FogColor not change?

I'm trying to make a script that changes the FogColor of Lighting when the ClockTime changes, however it produces no errors in the output.

local lighting = game:GetService("Lighting")

lighting.Changed:Connect(function()
    if lighting.ClockTime == 6.4 then
        for i = 1, lighting.FogColor.R do
            lighting.FogColor = lighting.FogColor + Color3.fromRGB(1, 1, 1)
        end
    elseif lighting.ClockTime == 18 then
        for i = 1, lighting.FogColor.R, -1 do
            lighting.FogColor = lighting.FogColor - Color3.fromRGB(1, 1, 1)
        end
    end
end)

Why isn't this working and how can I fix it? Please help!