@Rhiannon58 , so glad to see your response. And yes you will become a coloring fool the more you use CASt, lol.
Here's a help guide on it: https://www.carls-sims-3-guide.com/info/create-a-style.php
Not sure if you know this part or the above link shows this, but when one of your color channels is selected, you can grab it with your cursor (where it turns into a hand icon) and drag it on to whatever item you're wanting to recolor. This is useful when you are matching items with the same patterns/colors, it saves a lot of time. And you can also grab the little tab area just to the left of the first color channel, and it will grab all four of the colors at once so you can move it onto a similar object you want replicated. For instance, if you are recoloring a window, and you already have all of your windows placed and you change the colors of the first window, then you can just grab the whole color channel and move it onto each window and repeat. Saves you from having to do each window separately.
You can also click on the little "-" or "+" button that shows up on the bottom, to collapse color channels that are the same, that way you don't have to do each one over, if that makes sense.
One question that came to mind: how did you get those small rocks along the walkways to fit close together? The small rocks I'm using take up a square and I can't seem to overlap them.
I'm not sure if you've ever used the cheats, but for the rocks, I just turn on the cheats, "moveobjects on" and "disableSnappingToSlotsOnAlt on" to allow me to place things off the grids. Once this cheat is on, you hold down the "alt" key on your keyboard when grabbing the item to move. This is great for placing plants or moving furniture pieces closer together, but you have to be careful that you are not moving things in the way where your sim will have a routing issue, so you'll need to test areas at times. There are lots of cheats lists out there if you don't have a list, you can just google it. To bring up the cheat bar, you tap on the "ctrl shift c" on your keyboard (hold down all at the same time) and then you can type in the cheat commands.
Hope this helps.