You can use less hues/shades, and make the shape change instead. That's also easier to commit to memory. If a friend's avatar is a circle with shades of green/p

You can use less hues/shades, and make the shape change instead. That's also easier to commit to memory. If a friend's avatar is a circle with shades of green/purple, and another friend is a gem with shades of green/purple, the hue doesn't matter as much.