Clowsetum - Non-uniform Root Discoloration

[jiblylegs]

Hi all,

On this clowsetum (and I've noticed this with cattleyas as well) I am noticing some discoloration on two roots and it looks awful. It is potted in 100% sphagnum, and I water it with tap water.

You'll notice that for the first picture towards the base of the roots on the left is this odd orange discoloration. The picture on the right shows roots that aren't affected.

I know this is one of those frequent/mundane questions, but any ideas what is causing this and is it harmful? My only inkling of an idea is that it is not okay to even 'pet' some roots. I was sure not to bump these roots, but I have lightly felt/brushed them with my finger. This happened overnight after the first watering. At night it was perfectly white. Then by the morning these two roots were orange and have been progressively turning more orange.

I'm out of ideas. Thanks in advance!