Rusty red coloration on cattleya leaves.
 

Hello:

A few of my cattleya have this reddish coloration and it seems to be only on the newer leaves. Any idea what causes this?

That's common in some Cattleyas grown in strong light. It's a good sign.

This could be linked to it ----- (link)

Some compounds produced in the orchid as a response to relatively bright light for long enough periods of time ------ may just so-happen to make the colour of a leaf etc become different than usual ----- but the compounds also may have a beneficial effect, such as preventing the temperature in orchid leaf cells from getting too high ------ where the production (and existence) of these compounds can help disperse energy/heat to help prevent over-heating. This all works up to some point obviously ------ as the system won't work if the light energy is too much for it to handle.

That color in the leaves in bright light is particularly pronounced in plants with dark flowers. It is getting the upper range of the light that it wants - think "suntan". That level of light will encourage blooming.

Thank you.
 

Thanks to all for the intelligent answers, as a result, I have shaded my green house a little more.

I've seen this quite a bit with my cattleyas by now. Not all hybrids, like the cattleya free spirit is completely green no matter what but my potinara burana beauty is the darkest purple, it's almost black.
It's not all down to light, it really depends on the variety and strangely enough I have also seen orchid adapt to high light which really took me by surprise. Basically I stuck a vanda in a spot that turned it's leaves darker and initially I was playing a game of move the vanda whenever the leaves got too dark but I knew the light was fine for all my other vanda's so I decided to just leave it and see how badly it got burnt... A few months went by. It started growing like crazy and the new leaves... completely green.
To me I'd say it eventually adapted to a higher light condition and is now growing faster as a result but it took me probably a year before I decided to just ignore the dark leaves.


Anyway to cut a long story short, to me this one look like its getting the perfect light level. Less light will just result in the plant receiving less energy. You don't want to give any more either but this level is perfect so unless a prolonged heatwave is on the way I wouldn't change anything.