Balloons are one of those objects that seem deceptively easy for artists to draw. On the one hand, they aren’t complex shapes, but on the other hand, their coloring can be quite tricky. The material is often semi-opaque, letting just a little bit of light through while still having some shine. The round shape can make it a bit tricky for artists to color them realistically.
But the contrast of vibrant balloon hues and characters like Satoru Gojo (from Jujutsu Kaisen) can be rather fitting, don’t you think?