It's just a tip, you don't have to follow it strictly. I personally like to use 7 shades for one color when I'm spriting for fun, it's not very fit for Terraria so in that case I use 5 max.EDIT: I just finished one, and man is it hard for me to confine myself to less colors... I usually just change the shade whenever I need to and don't worry about how many colors I'm using.