How do you use distance and println to make two ellipses change color when they pass through each other?

Can someone give me a sample code? Pleasee helpp . I'm getting a headache from this . And this is what I have so far:


int xpos=100;
int ypos=100;
int xspeed=3;
int yspeed=7;
int xpos1=80;
int ypos1=100;
int xspeed1=4;
int yspeed1=3;
float distance;
float radius;
float diameter;
float value;
float r,g,b;
int x1;
int x2;
int y1;
int y2;
void setup() {
  size(400,400);
}

void draw() {
  background(255);
  if(distance>width)
  {
    fill(120,230,120);
  }
  radius=distance;
  distance=sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
  x1=xpos;
  y1=ypos;
  x2=width/2;
  y2=height/2;
  println(distance);
  ellipse(xpos,ypos,100,100);
  xpos=xpos+xspeed;
  ypos=ypos+yspeed;
  if(xpos>width)
  {
    xspeed=-xspeed;
  }   
  if(xpos<0)
  {
    xspeed=-xspeed;
  }
  if(ypos>height)
  {
    yspeed=-yspeed;
  }
  if(ypos<0)
  {
    yspeed=-yspeed;
  }
  fill(230,120,103);
  ellipse(xpos1,ypos1,50,50);
  xpos1=xpos1+xspeed1;
  ypos1=ypos1+yspeed1;
  if(xpos1>width)
  {
    xspeed1=-xspeed1;
  }   
  if(xpos1<0)
  {
    xspeed1=-xspeed1;
  }
  if(ypos1>height)
  {
    yspeed1=-yspeed1;
  }
  if(ypos1<0)
  {
    yspeed1=-yspeed1;
  }

  }