Class may need some refinement

Processing Coding Questions
1

Thank you for reading this.

I have created a simple LED class that, no doubt, needs some refinement. I thought about adding a capability to have square LEDS as well as a size option. I also wanted to have the colours as part of the class but that prevents me from including the colours in the constructor. It seems that the constructor parameters must be global variables and cannot be class members. Maybe a default colour?

Finally, and I just thought of this, can I import the class instead of including the code within the programme?

color red = color(255, 0, 0);
color green = color(0, 255, 0);
color blue = color(0, 0, 255);

int num_leds = 4;

Led l;

Led[] z;

void setup()
{
  size(300, 300);

  l = new Led(80, 50, red);

  z = new Led[num_leds];

  for (int i = 0; i < num_leds; i++)
  {
    z[i] = new Led(80 + (i * 40), 120, blue);
  }    

  l.on = false;
  //  z[0].on = true;
  //  z[1].on = true;
  //  z[2].on = true;
  //  z[3].on = false;

  frameRate(2);
}

void draw()
{
  if (l.on)
  {
    l.col = red;
    l.on = false;
  } else
  {
    l.col = green;
    l.on = true;
  }

  l.display();
  z[1].col = red;
  z[2].col = green;

  z[0].display();
  z[1].display();
  z[2].display();
  z[3].display();
}

class Led
{
  int xpos, ypos;
  color col;
  boolean on;
  //color red = color(255, 0, 0);
  //color green = color(0, 255, 0);

  Led (int x, int y, color c)
  {
    xpos = x;
    ypos = y;
    col = c;
  }  

  void display()
  {
    fill(col);
    circle(xpos, ypos, 30);
  }
}