The first time I read this post title from the forum and thought it was about the snooker pool. Surely, I was wrong!

The swim-pool is a complex build tool.
In my present idea:
It's at least graphically consisted of
1. pool-walls (some settings found in the scripts like wall.txt and deckfoundations.txt) (the pool bottom seems to be a level/story under the ground layer.)
2. caustic pool-tiles (the ones with the under-water caustic animation)
3. caustic pool-wallpapers (the ones with the under-water caustic animation)
4. pool-surface-tile (different models are used according to the types of the video cards, also) (the one I've released are just based on the basic model.) (at the toppest stage in the underground swim-pool room.)
5. poolsheet object (for water splashes, especially when sims using for the diving board)
6. pool-depth-layes (should only for the TS2 and UNI)(seemingly on different stages in the underground swim-pool room)

Note: "stage" I meant is something similar to the OFB stage foundation. And in the case of swim-pool, the stages' heights are fixated, probably just like the OFB stage foundation. The pool surface, also happens to be where the sims swim is the highest stage in the pool level room. The pool depth layeers are on ldifferent lower stages in the same pool level room.

Modding the swim-pool can be a moderate-big project. At least, doing some works on 2-6 are relatively easy for now if you don't mean to fully manipulate them all.

Note that the caustic effect animation is done by a caustic shader along with the caustic textures (search "caustic" and get them spotted out.)

The pool-surface shader is even more amazing, it can do sinewaves patterning along X and Y axies on the mapped surface to create a vibrating simulation. Say, a table that is made of such material can dance due to the sine vibration simulation if you can imagine what I mean. I know it coz I've made one but not released yet (I'm making a set...)! or check out this file
Numenor(MTS2)_SphereMatte_Moi_sphere_011-poolsurfacel-R0=wavy.rar
from here

As for the pool-wall, it's defined as a type of wall, so it has common properties and features from the wall tools as well as its own specified properties and features.

As for the colourations of pool-depth-layer-tiles and pool-surface-tiles are seemingly unfortunately predefined by their corresponding material shaders, so altering their diffusion coefficients won't help. Even worse, an upperstream parameter "colorScalar" doesn't seem to work either (a diffusion coefficient can be the value of the "colorScalar"). But, I can be wrong on some settings, so don't let my failures mislead you. Maybe, there're other ways, too.)
Anyway, if you feel like, you can write up your own material shader to alter the colouration that way.
(***Added***
Modifications on the material shader appear to work for the roof, so I assume this should work for the pool surface and pool depth tiles... Yet, a replacement global hack should work, but I suggest an additional mod is better for more possibilities. Unsurely, I may give a try to make reddish pool water for my bloody lust, happy Holloween.
***added***)
Yet, you can use the envcube map and recolour that map to your desired colours in order to affect the pool surface's reflection and refraction! That can help in certain amount of degrees.



I still fail to find the infos about linking all these elements together completely. I'm guessing the UI package may have some hints at the moment.

The following 2 posts are what I can do so far with the swim-pool tiles (2-4 and 6)
Settings for pool-tiles and pool-wallpapers: post34
Settings for pool-surface-tiles: post39

As for wall or wallpaper,
there's a little info about it here:
Modding - Wallpaper: wallMaterials_tslocator_gmdc (default wallpapers have meshes); Settings for bump-mapping; Update 2006-07
http://www.modthesims2.com/showthread.php?t=163016
but fooling around with the scripts can help gain some insights about the pool-walls
Modding InfoCenter - Partitions: walls, fences, fence arches
http://www.modthesims2.com/showthread.php?t=106473
and
deckfoundations.txt

also, may check out the attachment for the wall shader script.

As for doing the circular pool shape, the easiest and fastest means I think of is to do a curved "curtain" or window like Numenor's curved set of his wall-window collection (here ) You can use a curtain or window as the base (so, you can do both the diagonal and the straight walls). The later can have the lighting passage disabled, but this you may ask Numenor.
you can adjust different heights for the mesh for different positionings. Say, an undergound one for the default swim-pool. A wall-high one for a default wall height for the above ground "fake-pools" as described here
So, for an object-maker, a curvy-looking swim-pool is definitely possible...


These're all I can tell so far for now.

No worry about who has already started to do something, go ahead...
I may not be able to do further.
you can try to mod the swim-pool more or even translucent wallpapers, and blah blah blah... I tend to think such possibilities are there especially for those can programme or at least write scripts or mod the shaders...