I've been having a problem for a long time on my thick leaf orchids
(mostly phals, but now a dendrobium and another one). When you wipe the
leaves with a wet paper towel, red "dust" comes away. The leaves can
show this red dust too, but often on the bottom (and sometimes tops of
the leaves) there is white/brown stuff that can't really wipe away.

The leaves look really sickly.

Any ideas what sort of creature or virus I might have, and more
importantly, how I can stop this short of getting rid of all of the
beautiful thick leaf orchids?

Thanks.