inconspicuous way to cover a fan hole on cabinet

I have my cabinet all built and I need a way to cover the exhaust fan i have coming out the top of the cabinet

the exhaust fan is actually in the cabinet so its really just a 4" hole in the top....i dont want light to get in...but i also dont want some weird looking shit on the top of my cabinet

any ideas?

people use the black cloth from speakers to cover grow box holes

get 4 inch ducting, spray paint the inside black and put the ducting inside the cabinet and bend the ducting 90 degrees. connect the ducting to the exhaust and there you go!