Adrian Caspersz wrote:

it's a 2-pin. LED is driven across the outputs.


5v ---+----+
| |
R R
| |
| |
pin 2------+-----.
| |
| LED
| |
pin 4 +----------'

The manual does indeed say each pin has a pull-up resistor, and I would
expect it to pull down one pin or the other depending which colour it
want to show.

But why would the LED show one colour when on, but _not_ the other
colour when off? Given that both colours work, depending on which way
round I connect it ...