Cannot clear bundled cable output

The code i'm currently using is below. It is supposed to toggle on the blue output sleep and then turn it back off. I have looked through my code and i can't understand why it doesn't work. The output comes on but does not turn off. Ideas?

while true do
local cur = rs.getBundledOutput("left")
a = colors.combine(cur, colors.blue)
rs.setBundledOutput("left", a)
sleep(1)
b = colors.subtract(cur, colors.blue)
rs.setBundledOutput("left", :)/>/>
end

The "B" in the code is not a capital in my terminal, just something to do with the forums that makes B's capital.

This thread can be deleted, i am not using the correct code for what i want. I was missing a sleep value but that isn't going to help for my needs.