Multi coloured backgrounds processing

Multi coloured backgrounds processing

So I am SUPER new at processing, basically I am guessing how to do EVERYTHING. My final product I want it to be a gradient coloured background with a star moving around on it. 

I have the star, but I cannot figure out how to make a multi coloured gradient background behind it!  

This is my code:  Please help! 

void setup () { 
  background (43); 
  size (500, 600); 
  smooth(); 
}

void draw() {
  background(#B513E8);
  translate(mouseX, mouseY);
  fill(#13E8D8);
  stroke(255);
  strokeWeight(2);
  beginShape();
  vertex(0, -50);
  vertex(14, -20);
  vertex(47, -15);
  vertex(23, 7);
  vertex(29, 40);
  vertex(0, 25);
  vertex(-29, 40);
  vertex(-23, 7);
  vertex(-47, -15);
  vertex(-14, -20);
  endShape(CLOSE);
}