In a medium bowl, combine the mayo, mustard, vinegar and sugar. Stir well.
Using the large holes, grate both apples. Or cut the apple into matchstick pieces.
In a large bowl, combine the coleslaw blend and apple. Pour the mayo mixture on top and stir with a large spatula until well combined. Store covered in the fridge until ready to eat.
The apple slaw can be made several hours before you plan to eat and is best when made the day of. Leftovers can be stored in the fridge for 2-3 days, but the purple cabbage color will start to run.