To do Alt + H + S + O + M on Mac in PowerPoint, download and install Accelerator Keys, then press Option, followed by H, S, O, then M.
Command: More Outline Colors
This is how to do Alt + H + S + O + M on Mac in PowerPoint with Accelerator Keys, the native ribbon and alt key shortcut solution for Mac users who get more done with PowerPoint.
Alt + H + S + O + M opens the Colors dialog, allowing you to choose from a full color spectrum, enter specific RGB or hex values, and set transparency for the shape outline color.