After downloading a custom syntax coloring scheme, it is not automatically put to use.
All the schemes that you download are listed in the “syntax coloring” drop-down list on the Colors and Syntax page in the file type configuration. They appear in alphabetic order among the schemes that ship with EditPad Pro. This drop-down list is shown in the screen shot below.
To use one of the schemes, create or edit a file type, and select the coloring scheme you want from the Syntax Coloring drop-down list.