Colored OB PEX should have a gloss coating to it which is the barrier. 

I use the site Psychology Today as my referring source.

__________________________Provide the name and physical description (size, color, weight, license) of the animal:_______________________________________________________________________________Does the animal perform work or do tasks because of the disability?

Doing it this way may not be monetarily the best way to do it but it works better because you get a psychological reward of paying something off and it will then give you motivation to pay off the next. 

Do you just go with bland neutral colors (eg a coat of primer and grey/tope) or do you do something else?

You can't keep rent for months that you kicked them out.You could require that the walls be returned to the color and condition they were in when they vacate, and use the deposit to cover it.

This leaves borrowers vulnerable to rate movements, which can affect loan proceeds and other terms.Hope this helps provide some color on what options are out there! 

And that value is two-fold: firstly, you get the value of newly upgraded property (and you don't close until the rehab is done, so that vacancy time isn't on you), purchased at market price, that (if you finance) your tenants will pay 75-80% of over time; secondly, you get the psychological value of knowing that someone else has skin in the game, someone who absolutely knows what they are doing and has efficient systems in place to ensure you do as little work as possible while still collecting monthly income.

I have seen agents use colorful sticker on the cubical walls.

The problem I have is understanding the psychology of the seller (in pretax sale foreclosure )....