Colors Used in video:
(White / rgb(127,127,127) / rgb(128,128,128) / Black)
At the time of the video I thought it was only grayscale colors, but it applies to every color.
1.) Create a blotch of one color on an icon.
2.) Create a blotch of another color.
3.) And Another (If you want)
4.) click on one of the colors you have added inside of the "Colors in use" area and press delete.
Every color used in that state get replaced with what you have right-clicked in the used area.
The colors which you have selected, get replaced with that which you have right clicked (default: Mask)
Credits: Inushi & Myself