Year 5 Snowball Experiment

Year 5 were set the task to make a giant snowball in groups by collecting snow and packing it down into a hard sphere. We then made predictions before covering the ball in salt and food colouring. We had a range of interesting results and concluded that in some cases the salt dissolved into the food colouring and melted the snow quicker and in other cases it made the snow structure harder. Why do you think this is?