To do Alt + P T C on Mac in Excel, download and install Accelerator Keys, then press Option, followed by P, T, and C.
Command: Theme Colors
This is how to do Alt + P T C on Mac in Excel with Accelerator Keys, the native ribbon and alt key shortcut solution for Mac users who get more done with Excel.
Alt + P T C opens the Theme Colors gallery to change the color palette used throughout your workbook. Theme colors affect charts, tables, cell styles, and any formatting that uses theme colors, letting you quickly rebrand your spreadsheet.