Tygre there must be something wrong with AmiModRadio, as even when it's closed it doesn't let to rename or delete the images it has used.
Now for example I've made a script that selects a random Skin for AmiModRadio (also depending on the number of colors you use), but it doesn't work because it doesn't let me to rename or delete the skin it has formerly used.
So it only works selecting a random skin after each reboot.
Edit: But I see that even having as background a renamed MUIBackground.iff that now uses another image, MUI4 shows as background when you select it the same it was using at first. Yes, it's very rare, you open the image in the drawer and it has another image, but MUI4 selecting that image shows the one that was there at first, not now.
Edit2: I've been told it can be made (random background), but it's too difficult for me.
MUI uses datatypes.library to load the images. It is datatypes.library which keeps a lock on the files as long as the images are in use. Furthermore MUI caches the images. So it is very probable that the lock on the image file will persist even after AmiModRadio has terminated. Just flush muimaster.library from memory (i.e. by using FlushMUI) to remove and unlock all currently unused but cached images.
And I never said you should rename your images externally and keep on using a fixed background spec. Why offload the random background selection when it can be done much better internally?
I suggested to pick a random file name and generate the background spec dynamically. For example:
Provided you have 10 images named image0.png to image9.png this will dynamically set one of these as background image in a random fashion.
snprintf(backspec, sizeof(backspec), "5:path/to/your/images/image%ld.png", rand() % 10);
set(object, MUIA_Background, backspec);
If you still need different font outline colors as you said before you need to keep an additional mapping between background image and font outline color to let them match as you require it.
Edit3: Ups. I forgot to comment that I've made for my next AKReal 860 update a new option with MorpheuZ, so you can select among some different (6) AmiModRadio MUI4 setups. This is a screenshot using RTG -on AKReal you just need to use "Better Config" in Tools and click twice to switch to RTG-: