Here is a pic. of part of my collection grown outdoors all year under shade-cloth.
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If you go around looking at individual plants you find some with those reddish purple tones on the pseudobulbs and on the leaves. Must come from one or more species used to make the hybrids.
Too much light (and maybe heat stress) is indicated by washed out looking yellow lemon coloured leaves.

This post was edited by arthurm on Fri, Feb 22, 13 at 1:46

Arthur, should I conclude that the purplish color might be from not enough light then? I can put it closer to the window. Guess I need to put the catts on the shelves farther from the light fixture.

No! I do not think it is about the light. Lack of light is almost never a problem here. So, out of hundreds of Cattleyas i found some here and there that had the reddish tinge on leaves or pseudobulbs. Maybe it is genetic and needs something like being slighty too cool in winter to appear.
I'm not fretting about it because otherwise the plants appear healthy.
Again, not much help because i know nil about growing under lights.

Nearly all the Catts grown by hobbyists today are hybrids. Some Catt species have reddish-edged leaves leaves, this may be inherited by some of their progeny. Be worried by yellow blotches however.This is nearly always a sign of rot. Too much water? Too moisture-retentive a medium? Too low a temp (60-80)/ combination? It is really hard to keep Catts in good condition in Zone 4. I wouldn't be watering them at all in winter unless you have a very sophisticated heating/ humidification system.

ianbrazil: sounds pretty drastic to not water them at all! I've recently repotted all the catts in clay balls and the roots looked fine.

The picture in the post above was taken in sunlight under 50% Shade-cloth at latitude 33 something south in July (winter)
I do not think traces of red are a problem provided the plant looks healthy and blooms.
Seeing there is another another thread hereabouts asking the same question maybe it is time to pass the puzzle over to under light gurus by describing what type of lights you are using.

Now I'm more worried about the yellow blotches than the reddish shading! Why does everyone think orchids can't grow in Vermont?

Of course you can grow orchids, anywhere, but i was just wondering if the light provided by artificial lights might promote the red tones in some Cattleyas.
I speak about the washed out lemon yellow tones from experience when i delayed putting on the extra layer of shade-cloth in spring.
Maybe it is possible to put your plants too close to the lights?
Sorry, that you are not getting advice from real orchid growers. I looked up the climate zones the other day and the micro-climate in the yard is zone 10.

Maybe you should post a picture of the leaves? I grow under lights and in the window sill. I have noticed purple and red coloration on my catt leaves because they are too cold and when I have them too close to the lights. So it could be either of those. I don't worry about the purple/red spots. I doubt that you should either. Now for the yellow spots. There is always the possibility of something sinister happening with your orchids. But if the spots are not soft or sunken inward, I would not conclude that there is a rot problem. However, I doubt that too little light is an issue either. I am wondering there is too much light and the yellow blotches are the beginning of sun burn. Without looking at them these are all just guesses.

Overall, you have said that they are growing well and the roots are healthy. Considering these things, you are probably fine. If you are concerned about growing orchids in your area, try to find a local society. If I can grow in cold cloudy Northeast Ohio, Vermont should not be a problem.

Also, I water my catts year round. Unless you have species that requires a dry rest, continue to water. Just not as much if the room is cool/cold. They can stay drier but don't let the pbulb start to shrivel.

A couple of additional questions. What kind of lights do you have? Are the yellowing leaves occurring under the lights or in the window? That information would help.Still if the plants are growing well and the roots are in order, I would not worry. especially if the spots are not soft or anything like that.

Hello Andrea:
I guess you did not know that there are orchids societies near you with members that would love to analyse your problems. New Hampshire Orchid Society ( http://www.nhorchids.org/ ) just had a show in Nashua and Amherst Orchid Society just had a show this weekend. People bring their questions and members swarm around with good advice! Twin State Orchid Society is in VT too, but they have not put on a show.

The purple on leaves is anthocyanin and related compounds that protect the plant from too much light. I wouldn't worry about it. Likely, extra sun at this time of year is good, and would encourage flowering in the future.

Yellowing of leaves could be the result of a number of things. Insect pests, root rot, fungi, or just aging of the leaf. Without seeing the actual plant, it's hard to tell what is going on. Is it on just a few plants or the majority?
Is been pretty gray this winter- sometimes lack of sun or too cool a temperature makes a leaf konk out.

If you think it is root related, then inspect the inner media - is it breaking down and composting? Then get it into fresh media as soon as you can, removing the rotted roots.

Inspect for pests and take measures.

Good luck!

Maryanne in WMass

Here is a link that might be useful: Amherst Orchid Society

Thanks to all who provided such thought-provoking information and questions. I'll get to posting some pictures soon, but briefly, the roots all seem fine. As I said, I've repotted the catts into clay aggregate recently so I had a chance to inspect them. I'm inclined to think I shouldn't keep the catts directly under the fluorescent light fixture, so I've moved them down one level. The one with the purple cast to the leaves is a big monster and is next to a window. As Arthur speculated, the leaf color could be hereditary. I'm glad to hear that gray, cloudy weather is found in other orchid growers' states! As for orchid societies, there was one in the Burlington area but it folded in the past year or so before I got a chance to check it out. I should have gotten myself over to Nashua for that show.