How to set multiple colors to transparency using Microsoft PowerPoint

Powerpoint has a feature to set one color to transparency
http://troubleshoo.blogspot.com/2017/03/powerpoint-2016-machow-to-set.html

To set multiple to transparency, you will need to do it sequentially:
1. set one color to transparency
2. save this image to a file
3. import back the saved image
4. go back to step 1. for another color