BitmapData setPixel() some times results in black pixels?

[Raicuparta]

I'm making some BitmapData squares, and painting each individual pixel randomly, like this. It works like 90% of the time, but for some reason, some times, it generates something like this.

The code that generates the BMD:

  generatePattern (size) {
    let pattern = this.game.make.bitmapData(size, size)
    for (let x = 0; x < size; x++) {
      for (let y = 0; y < size; y++) {
        let color = this.randomColor()
        pattern.setPixel(x, y, color.r, color.g, color.b, true)
      }
    }
    return pattern
  }

I then use the generated BMD as textures for my sprites with Phaser.Sprite.loadTexture()

I know it's not a problem with the way I'm generating the color, since even if I try to just set the RGB values to 255 255 255 (skipping my randomColor function), the problem persists. So it seems to be something related to the setPixel function.

Using Phaser CE 2.8.0