I pruned orchid to remove spent stems but now one leaf is all yellow. Should I remove it?
Inspect your Orchid for any signs of pests or disease.
Yellowing leaves can also be due to watering issues.
Pruning can be done after your Orchid is done blooming and your plant will need a dormancy period. Make sure you use clean, sterile tools while working with your Orchid.
Here are some links with more information.