alpha channel not working for me

[alejandroLoz]

I'm trying to transform the background into transparent but it's not working for me:
I've tried context.fillStyle = "rgba(0,0,0,0)"; but it fills the background with a non transparent color.

What should I do?

[alejandroLoz]

Checking the code if found this:
color.a = Math.round((parseFloat(vals[3])||1.0)*255);
So in case of setting vals[3] = 0.0
parseFloat(vals[3])||1.0) returns 1 which turns the alpha value to 255.