I'm curious about this as well. I'm new to designing watchfaces and may just be overlooking something, but I've been doing some experimenting with one of my watchfaces, which can be viewed here. I'm wanting the end-users to be able to tap on the watch and change the watchface color to whichever color they want from the colors I've made available to them. I realize it'd be far easier to just create the individual colored watchfaces as separate designs, but if it were me and I wanted blue one day and orange the next, I'd prefer to have the option to change colors in a single design by tapping it rather than having to change the watchface altogether.
As of this post, I've uploaded 5 separate images (each with their own color), and in each image's transparency setting I've used this conditional (changing "=1" so each picture has its own number):
If I'm wrong, then someone please help me out, but this is the way I interpret this conditional:
When the watchface is tapped, one of five possible random numbers is generated.
If the number generated is equal to 1, then transparency = 100%; otherwise, transparency = 0%.
What I have observed thus far isn't very promising for what I'm trying to accomplish, and it appears there are two things I don't like about this conditional. One is what @apalileo said about how "the swaps [made by the stRand(min,max) function] are not consistent". Instead of accomplishing what I mentioned above about the end-users being able to tap and select the color they want, I'm finding that the random number generator somehow generates the same number consecutively multiple times before it will finally generate another number. In other words, if the current image is on orange and I want to change it to another color, then I tap on the watch to change it. However, instead of it changing to another color, it stays on orange for, say, 3 more taps before it finally changes to another color. The second thing I've noticed that I don't like about this conditional is that the watch is on one color when it's active, but then when it comes out of dim mode it's on another color. So again, if I'm wanting my end-users to be able to choose a color that they like, going to dim mode seems to automatically change the color even without it being tapped, thus making their color choice irrelevant.