Ensure pdfBackground constructor property is used #4207

Slightly refactor the way background colours are set

lib/operation.js

@@ -3,7 +3,6 @@
 
 'use strict';
 
-const color = require('color');
 const is = require('./is');
 
 /**
@@ -67,13 +66,7 @@ function rotate (angle, options) {
   } else if (is.number(angle)) {
     this.options.rotationAngle = angle;
     if (is.object(options) && options.background) {
-      const backgroundColour = color(options.background);
-      this.options.rotationBackground = [
-        backgroundColour.red(),
-        backgroundColour.green(),
-        backgroundColour.blue(),
-        Math.round(backgroundColour.alpha() * 255)
-      ];
+      this._setBackgroundColourOption('rotationBackground', options.background);
     }
   } else {
     throw is.invalidParameterError('angle', 'numeric', angle);