Villustrator and Vivify
Villustrator (GitHub: bilalq / villustrator) by Bilal Quadri is a web service for generating Vim colour schemes. It has colour pickers and the results are displayed dynamically. It’s also open source, feel free to fork it and add new features.
This apparently inspired the creation of Vivify, which is a more in-depth web-based colour editor. It shows samples of various programming and markup languages, and supports both GUI and text mode previews. It even has more advanced colour manipulation features, with hue and saturation cycling.
The cool thing about Vivify is language constructs can be selected with the mouse, and it’ll show the highlight name Vim uses to colour that element. This makes understanding Vim syntax highlighting a lot easier.