To change an icon’s color, you must first select it before inserting into your presentation or document. After selecting an icon, select the color dropdown menu. Alternatively, select 'Custom Color'. This will allow you to refine your color selection or allow you to enter your desired HEX, RGB or HSL values. If you do not see the color input boxes you may need to widen your add-in window to find it on the far right side of the screen.
For Pantone color options, first convert your Pantone color to HEX or RGB, then paste into the custom color field. Here’s a free and easy tool made by Pantone to convert accurately: https://www.pantone.com/color-finder/