A new update is here for AudioTheory Piano Keys. This adds in the ability to change the note colours, and the application can now be customised to use any combination of colours you desire.
The new .ini file
Once you've updated to AudioTheory Piano Keys 1.5.0 then the first time you run the application it will create a new 'Data' folder inside the application's directory folder. The easiest way to get to this is to then right click on the app in your Steam library and select 'Manage --> Browse Local Files'. If you're on a Mac the location of the folder is a little different and it can be found in the Application Support folder. So just to clarify where this file lives:
Windows and Linux {path to steam app}/AudioTheory Piano Keys/Data/
Mac ~Library/Application Support/com.DraculasCave.AudioTheoryPianoKeys/Data/
Open up the Colour.ini file in the text or code editor of your choice and you can then override the default note colours by changing the hex codes to specify the colour for each note. Changes will then take place the next time the application is loaded.
If you want to revert back to the original colours then the easiest way is just to delete the Colours.ini file and then the application will make a new one automatically with the default values.
A few other bug fixes have also made it into this update, but nothing too wild.