On our original example we can change the background color alpha to 0 and it works:
the code use the mix function,
i don't want use mix,because i only want show a color ,don't want mix other color
I am not sure then - but mixing a 0 alpha background works to hide the background. Sorry, we are not really supporting shader code - as we do not know enough about it. You might find guidance somewhere else. But it does seem that you can hide the background in this example in that way.
ok,thanks