I'm wondering how the progress bar in Super Hexagon was made. (see image, top left) Actually I am not very sure how to implement a progress bar at all using OpenGL ES 2 on Android, but I am asking specifically about the one used in Super Hexagon because it seems to me less straightforward / obvious than others: the bar changes its colour during game play.

I think one possibility is to use the built-in Android progress bar. I can see from some Stackoverflow questions that you can change the default blue colour to whatever you want, but I'm not sure whether you can update it during the game play.

The other possibility I can think of for implementing a progress bar is to have a small texture that starts with a scale of 0 and that you keep scaling until it reaches the maximum size, representing 100%. But this suffers from the same problem as before: you'll not be able to update the colour of the texture during run-time. It's fixed.

So what's the best way to approach this problem?

*I'm assuming he didn't use a particular library, although if he did, it would be interesting to know. I'm interested in a pure OpenGL ES 2 + Android solution.