Themes

Code themes

You can change the editor's code themes from

View -> Code Theme

Skins

You can re-skin ShiftEdit from

View -> Skins

Custom themes

You can edit your own skin and code theme from View -> Custom Theme

Then select it:

View -> Code Theme -> Custom

You can base your custom theme on one of the existing editor themes, see:

https://github.com/ajaxorg/ace/tree/master/lib/ace/theme