Hey there! It appears that one of the pseudobulbs has been compromised. If you look at your plant, the leaves in the back are still a really nice rich green, while the leaves in the front are looking a bit sad. I had this happen to one of my seedling catts in a very similar fashion. It turned out that one of the pseudobulbs had damaged roots. The leaves from that p-bulb slowly shriveled and died, and eventually I just pulled that p-bulb out so that the rotting parts didn't bother the rest of the plant.

The good news is that it appears you have at least one VERY healthy pseudobulb toward the back of the pot, if not two. You are most likely going to lose that yellow and brown leaf, and you may lose whatever other leaves are attached to the damaged bulb. But once that happens, the damage should stop there, and the remaining bulb or bulbs will continue to put out new growth and fill out the pot. Eventually you'll have a big, healthy plant with multiple bulbs, and you won't even remember the one bad bulb you lost early on.

Just be careful not to over-sun this one. It appears to be a seedling, and they're fairly delicate and need to be slowly acclamated to full catt light levels. Also, be extremely careful not to let it sit in wet sphag. I personally don't like sphag at all...things rot way too easily in it. Catts like to be potted up in bark, not sphag, but yours is probably in sphag because it's a seedling and doesn't have the water storage capacity to survive very long in bark. Unfortunately, sphag can very quickly rot your roots.

This is what I would do if it were me: I would get the plant out of the sphag, put it in some fine bark, and put the whole pot in a terrarium-like structure. The terrarium (you could use anything glass, really, that the little pot will fit in) will keep enough humidity around the seedling that it will be okay in the bark. I would water it every couple of days, when the bark is dry to the touch. When you start to see new growth, you can take it out of the terrarium (or whatever you're using...fishbowl, fat vase) and put it in your regular grow area with your other plants. Be stingy with the sun at first...this is a delicate little guy and needs a while to toughen up before it will take full catt light.

But once the new growth gets going, it should be fine. The other reason I'd get it out of the sphag is that you won't be able to see the new growth starting, because it will be buried in the sphag, and there's always a chance your new growth will rot before it pops out of the moss. If you put it in fine bark, you'll be able to nudge the bark aside and see when new growth is beginning. Then you can sort of push the bark out of the way of the new growth so that it gets air and doesn't get soggy.

The good news is that this damage isn't going to kill your plant...you might lose a bulb, but the plant has others to compensate. If you treat it well, you will be rewarded with a lovely, full plant in a couple of years!