I want to see the colors of the map for current time, so from the Main Window I click "Timezone Info" and then "Calculate Map Colors"

I click the "Now!" button and click "Generate Map Colors" button:

Now the map is displayed with the current colors, for instance US is having five visible colors: Alaska in light gray for GMT-9,  orange for GMT-8, lime green for GMT-7, gray for GMT-6 and light yellow for GMT-5.

But I want to see the world time for 1.st. of April 1945 at 0:00. I close the map (upper right corner), and put in that date:

and then I click "Calculate Map Colors" to get the following map:

When I'm finished checking 1945,  I don't want these colors to show always in the map, I prefer the current colors, so I click the "Now"" button again, click "Calculate Map Colors" and I'm back with the colors for current time: