int rectCount = 5;

// syntax:
// type variableName[] = new type[arrayLength]
color rectColors[] = new color[rectCount];

void setup() {
  size(512, 200);
  randomizeColors();
}

void draw() {
  background(255);
  noStroke();
  rectMode(CENTER);
  
  float spacing = width / rectCount;
  float paddingLeft = spacing / 2;
  
  for (int i = 0; i < rectCount; i++) {
    fill(rectColors[i]);
    rect(paddingLeft + spacing*i, height/2, 50, 50);
  }
}

void randomizeColors() {
  for (int i = 0; i < rectColors.length; i++) {
    rectColors[i] = color(random(255), random(255), random(255));
  }
}

void mousePressed() {
  randomizeColors();
}