There are several different ways you could go at it. If you want to keep it easy to convert back to "swimming pool" and keep the cost down for both factors, here are some suggestions. Leave the color as is, the blue isn't that big a problem with algae and a black swimming pool might not be as easy to sell. Some shade for the pool will help against the algae as well as would having it coated in black. Let the water age to get rid of the chlorine. (What source of water do you have for re-filling if you were to need to do any water changes? If you have city water with chloramine you might need to look into some water conditioner.) What is your existing pool pump/equipment? In some arrangements, you could simply continue using the existing pump/filter. Or you could shut down and drain (like for winter storage the pump and sand filter, if you do this properly, the equipment can be hooked back up when wanted for a pool again.) Then you can get a submersible pond pump and a bio falls basin. Put the pump in the pool and hook up to the bio-falls basin sitting on the edge of the pool and you are set to go for small numbers of fish. Add some aquatic plants (make sure they are in large plant baskets with gravel, no dirt.) Place potted plants around the falls tub to dress it up a bit and away you go. Now this might not turn your swimming pool into a perfect ornamental pond but it is the cheap way to do it. Make sure to choose an energy efficient pump as you will probably be running it 24/7. In warm water you need to keep it flowing or the fish can run out of O2. It is best to start out with smaller numbers of smaller fish and keep the feeding light until the system has stabilized. Now if you want to make it really fancy, it will of course get more complex and costly. If you want large or lots of fish, then you will definitely need to learn more about Aquaponics, bio filtration, fish keeping etc. Here is a link that might be useful: www.TCLynx.com

Consider tile porousity and water absorption. Water absorption can cause freeze/thaw spalling issues, etc. When installing, use a full coverage of thinset behind the tile. No voids. Surface texture. Glazed tile would be considered more sanitary than a textured stone, there's less of a chance of floating debris collecting, drying, and creating a "scum line" at the water line. With all that written, I'm in New England, I have a tight-grained slate as my waterline tile. No issues over 15 years. Maintain your water quality and you'll be surprised how few issues you'll have with your pool. Clean and properly balanced water makes pool life easy. Good luck.

White based plaster finishes don't compliment natural materials, such as your flagstone choice for the coping. Mind you, my opinion. Plaster finishes in the gray scale look best with natural stones and tiles that are of the same color scheme. Grout choices should be also in the gray scale. with gray grouts. NOT WHITE!!!! Glass tiles with blues, greens, grays (light and dark) look fantastic . Click on my Houzz page and see the photo is a gray Hydrazzo Hatteras Gray with Limestone coping and glass tile with aforementioned glass tile 1x1.

I totally agree about the safety issue it can cause with children. We were suppose to have a raised bed back there but it’s been a nightmare to get both the pool builder and landscaper back out. The design of the pool is like that due to the easement line on the back of our property. Thank you for your feedback. We’re leaving towards adding additional decking back there.