One quirk that I really like is when a futa's cock has colors and features that clearly distinguish it from the rest of her body. Pic related is a very good example.
>most of the futa's body is white
>her balls and cock base have a little dull color
>as you travel up her cock, it transitions into being a bright purple and indigo.
Having the futa cocks be very moist, shiny and colorful really helps to illustrate that what you are looking at is a very sensitive sexual organ.