I'm no artist, but I had fun with Colors 3D. Even though there are a couple things I wish were incorporated that were not, checking out the gallery made me realize the potential of this program. For only $6.99, it's definitely one to recommend to pass the time if you like to draw and paint.
Though lacking in any type of structured play, Colors! 3D's robust free drawing system and unique ability to let anyone create their own three-dimensional artwork more than make up for this.
And for those of you who do and who want to get a little drawing time in, you can't really go wrong with Colors! 3D. It's available for a reasonable price – $6.99 in Nintendo's eShop – and allows you to put your 3DS to use honing an actual useful skill.