drawRainbow3

final int RED        = 0;
final int ORANGE     = 1;
final int YELLOW     = 2;
final int GREEN      = 3;
final int BLUE       = 4;
final int INDIGOBLUE = 5;
final int PURPLE     = 6;

int COLORMAX = PURPLE;
float dr = 0.0;

void setup() {
  size(400, 400);
  smooth();
  rectMode(CENTER);
}

void draw() {
  if (mousePressed == true){
    noCursor();
    noStroke();
    translate(width / 2, height / 2);
    pushMatrix();
    for(int i=RED; i<COLORMAX; i++) {
      fillRainbowColor(i);
      rotate(radians(dr));
      rect(mouseX, 0+(i*5), 35, 5);
    }
    popMatrix();
  } else {
    background(255);
    cursor();
  }
  dr += 8.0;
}

// 引数に対応する虹色のいずれかで塗りつぶす
void fillRainbowColor(int count)
{
    int check = count % (COLORMAX+1);
    switch(check) {
      case RED:
        fill(237, 26, 61);
        break;
      case ORANGE:
        fill(255, 183, 76);
        break;
      case YELLOW:
        fill(255, 212, 0);
        break;
      case GREEN:
        fill(0, 128, 0);
        break;
      case BLUE:
        fill(0, 103, 191);
        break;
      case INDIGOBLUE:
        fill(35, 71, 148);
        break;
      case PURPLE:
        fill(167, 87, 168);
        break;
      default:
        fillRainbowColor((COLORMAX+1)+check);
        break;
    }
}