Replacing drive with yellow light?

I have a 5D that is getting low on space: one drive is yellow. I would like to replace it with a larger one but question the statement on https://myproducts.drobo.com/retrieve/s3/knowledge/AA/AA-00909.html where it says:

How to add or replace a drive
Follow these steps:

  1. Ensure that all drive bay indicator lights on your Drobo are solid green.

Warning: If the drive bay lights are alternating yellow and green you must wait until solid green.

It says ensure the lights are solid green, so how do I replace a yellow drive (or is that statement wrong?)

Yellow means drive is near full. Seems OK to replace the drive.