Thanks! It seems to work, even if it took me 2 hours to make it work in a batch file 
One question:
I tried adding the "-resize 250x250" flag to the composite command, and also to the "load" commands, but at best it wasn't resized, at worst it crashed the batch file.
How could I do it? Thanks in advance!
Also, is there an option to dynamically darken a given rgb value?
Because I want to input only one color:
- the centered foreground would be in that color,
- but the offsetted one would be in a darker version of that.
One question:
I tried adding the "-resize 250x250" flag to the composite command, and also to the "load" commands, but at best it wasn't resized, at worst it crashed the batch file.
How could I do it? Thanks in advance!
Also, is there an option to dynamically darken a given rgb value?
Because I want to input only one color:
- the centered foreground would be in that color,
- but the offsetted one would be in a darker version of that.