Originally, my idea was going to be a revision of an old suggestion.
The older suggestion featured all the current colors being free (Gray, Orange, Blue, Green and Purple), the color wheel being a Pro Basic feature instead of Pro, and the addition of profile pictures, where they would be a Pro feature. My revision would include the new colors (Yellow and Red) being free too, as well as introducing non-pixelated icons, where they would be a Pro Basic feature.
However, people would abuse non-pixelated icons and profile pictures to create inappropriate things. And so, the ideas were scrapped in favor of this safer alternative. Now that profile pictures were removed, there had no Custom Icon features behind Pro, and so, the color wheel was moved up to the Pro tier, and the secondary colors were moved up to the Pro Basic tier.