Awww, this was both really cute and nicely done! I loved how you explained how Toph's mind works when it comes to colours. It was just a fantastic insight into Toph Beifong.
I love the use of purple too! Using the real world equivalent that purple was a royal colour rarely scene and usually only kept for emperors. Sokka choosing that due to the uniqueness of Toph, the idea that she's a rare find and that's he's lucky to have found her.
Fantastic job!