Copy color labeled photos from nested folders into one folder (action? batch?)

You could write a script to walk all the folders and only copy the red labeled ones. I'd just go with manual search, myself. Use the Find command.

There may be a more concise solution but this should work.

Select the uppermost or parent folder then View>Show items from subfolders. This will display everything. Then in the Filter Panel you can filter on red labels. You will then see the desired images. Select all then copy and paste to your desired folder