Hello guys,
I am VERY fresh with processing so please be gentle.

I am having a great trouble with this task.
I need to do a volume bar - black rect and inside 8 green, 8 yellow and 8 red bars. Bars are drawn when keyPressed.

The problem is with background. In my project background must be in draw().
I've tried many versions but can't resolve it :(

This is what I want to do, but with bg in draw()

 //line position on x axis
  int x = 237;
  //line position on y axis
  int y = 445;
  //lenght of line
  int len = 12;
  //spacing between each line
  int spacing = 6;
  //value on x axis where green lines end, after that display yellow
  int endGreen = 285;
  //value on x axis where yellow lines end, after that display red
  int endYellow = 333;
  //value on x axis where red lines end
  int endRed = 381;


void setup() {
  size(600,500);
  background(255);
  frameRate(15);
}


void draw() {
  //draw big rectangle
  noFill();
  stroke(0);
  strokeWeight(6);
  rect(230,440,152,22);
  //draw line
  strokeWeight(4);
  strokeCap(SQUARE);
 
 
    //if key pressed, display green lines one at a time
    if (keyPressed == true) {
     
       //display green lines for 8 lines
       if (x < endGreen) {
       //draw line
       stroke(0,200,0);
       line(x,y,x,y+len);
       //increment by 6
       x += spacing;
       //change color to yellow at x,y position
       } else if (x < endYellow) {
         stroke(255,255,0);
         line(x,y,x,y+len);
         x += spacing;
         //change color to red at x,y position
       } else if (x < endRed) {
         stroke(255,0,0);
         line(x,y,x,y+len);
        x += spacing;
       }
     }
}


I'll be greatful for your help.