Hi everyone i'm new on processing, and I can't get a good trasparency effect, if you try my example you will notice that where the spheres intersect the transparency is not always working. Can be solved? what i'm doing wrong?
Thanks .

1. import processing.opengl.*;
   
   
   float rotation=0;
   
   void setup() {
     size(800, 800, OPENGL);
     background(255);
     smooth();
   }
   
   void sensor_position(int number){
     noStroke();
     pushMatrix();
     if (number==1){
                   fill(0,255,0,255);
                   translate(12.5,+12.5,-12.5);}
     if (number==2){fill(255,0,0,255);
                   translate(12.5,+12.5,+12.5);}
     if (number==3){ fill(0,0,255,255);
                    translate(-12.5,+12.5,0);}
    
     sphere(1);
     popMatrix();}
   
   void draw() {
     background(255);
    
     //lights();
     float orbitRadius= 50;//mouseX/2+50;
     float rotation=mouseX;
     float ypos= 20+mouseY/5;
     float xpos= cos(radians(rotation))*orbitRadius;
     float zpos= sin(radians(rotation))*orbitRadius;
    
     camera(xpos, ypos, zpos, 0, 0, 0, 0, -1, 0);
     noFill();
     stroke(0);
     box(25);
      
     sensor_position(1);
     sensor_position(2);
     sensor_position(3);
    
     
     fill(0,255,0,20);
     noStroke();
     pushMatrix();
     translate(12.5,+12.5,-12.5);
     sphere(20);
     popMatrix();
    
     
     fill(255,0,0,20);
     pushMatrix();
     translate(12.5,+12.5,+12.5);
     sphere(20);
     popMatrix();
    
    
     fill(0,0,255,20);
     pushMatrix();
     translate(-12.5,+12.5,0);
     sphere(20);
     popMatrix();
   
   }