Know this is old but I thought I'd just chime in here as this was doing my head in!
I was seeing the exact same thing and no change in the code seemed to fix it.
It was barely noticeable on the red channel, but very noticeable on green and a bit less on blue.
Anyway, I was using a 12V 1A adapter and even though the strip i was using should have been drawing less than that, when I swapped it for a 6A unit, all flickering ceased.