I just added support for RAD Studio XE8 to the Delphi IDE Theme Editor (1.8.1.0). 
Also a new feature was introduced to allow edit the values (color and font) of the modern theme (only available in XE8). To use it just press the button “Additional Settings” and set values for the Main ToolBar and the IDE Font, finally press the button “Apply”. Also you can restore the default settings pressing the button “Restore”. 
Screenshots
You can download the DITE from here
