hi.  

i am drawing lines to the screen based on camera input and fading them by drawing a rectangle the same size as my sketch with an alpha value (say, 15).  this does not however, seem to be getting me back to white (255, 255, 255, 100 [presumably]), and instead the lines "fade" to a barely there dull gray.  

here is a a little test file that shows the same problem as my code:   

// test_fade
int fadeAlpha = 15;
int lineAlpha = 70;

void setup() {
 size(200, 200);
 background(255);
 strokeWeight(4);
}

void draw() {
 //print("FADE ALPHA:  " + fadeAlpha +'\n');
 noStroke();
 fill(255,255,255, fadeAlpha);
 rect(0,0,200,200);
 stroke(0,0,155, lineAlpha);
 
 if(mousePressed) {
   line(mouseX, mouseY, pmouseX, pmouseY);
 }
 
 if(keyPressed) {
   if(key =='u'){
     fadeAlpha = fadeAlpha+1;
   }
   if(fadeAlpha >100){
     fadeAlpha = 100;
   }

   if(key == 'd'){
     fadeAlpha = fadeAlpha-1;
   }
   if(fadeAlpha <= 0){
     fadeAlpha = 0;
   }
 }
}

does anyone know why this doesn't work to fade the background to white?  or how i can change it to fade to white?