If you tile on the drywall the drywall will need to be green or purple faced. Then need to apply 2-3 coats of redguard (red)or hydroban (green) either are waterproof latex paint applications. You can also do this too cement board. Cement board gets 1/2” not 1/4”.

You say this is a free standing tub-- is there a showerhead involved? If not, no need to waterproof, although it wouldn't hurt.

This is only a free standing soaker tub, so it will be held two inches or so from the walls. I’m only worried about moisture from steam and possibly light splashes on the wall. Can I use is Redgard recommended to use on the green board, or if I am going to use the Redgard do I need to use Durock? The shower is completely separate, and I am using a Kerdi system for the pan and up the walls a few inches, then using Redgard the rest of the way up to the ceiling.

I hate to tell you this but you did not have space for a free standing tub how on earth are you going to clean around that tub you need at least 12” on all sides and even then you will need to be in the tub to clean the back wall you have no way of doing that with only 2”

Patricia, thanks for going way off topic here. I’m not limited to two inches around the tub, I just threw the number out there. Do you have advice on the construction project I’m working on in regards to waterproofing or moisture?

Unless you're using boiling water ( :-) ), there's no way you're going to produce enough steam to cause damage, even long term. As for the Redgard, yes, you can use it over sheetrock, no matter what color it is.

I hate to tell you this but you did not have space for a free standing tub how on earth are you going to clean around that tub you need at least 12” on all sides and even then you will need to be in the tub to clean the back wall you have no way of doing that with only 2”

Waterproof the hell out of the walls.

Mark, I hope you don’t use run on sentences like that when emailing customers, because it makes you sound unintelligent. This is not a design post, it is a post about general construction and where I need to be concerned about waterproofing. Where am I going to find a faucet that protrudes from the wall 12”? The tub is tapered, leaving plenty of room to clean around the base, even if it were only a few inches from the back wall, like hundreds of soaker tubs are pictured on Houzz.

Thank you to those who have given me valuable information on waterproofing around my tub, that I will most definitely be able to clean around.

Where am I going to find a faucet that protrudes from the wall 12”?

My understanding is that in this case one uses a floor-mounted faucet (example).