4 Shapes Touching--Combined Version

We all are, jranders! I knew this puzzle would be a hit, even though it's nothing but 4 shapes with the very uncomplicated design of being stuck together so they touch! But that is always popular, and I know I love solving that kind, too--maybe it makes us feel safe and young and with our world in a very familiar order...

What is it about primary colors that is so appealing? I'm such a child -- isn't it fun?