Summary

Here is a Charizard coin that I made following requests for 'MORE' after my Zekrom coin.

My Zekrom coin: https://www.thingiverse.com/thing:5788818

In order to allow for printing in multiple colors, I layered this design in 3x equal slices of 1mm each:
1st slice = Charizard evolutions
2nd slice = solid layer
3rd slice = Pokeball and logo

I recommend printing the middle layer in a different color for the best effect (or 3x different ones like shown here). I recommend using a contrasting color in the middle to make the design 'pop' (and so you can read the back).

After actually printing this in 3x colors:
I MANUALLY paused at ~20-25% to change colors for the middle layer, and I waited until around 70% for the last layer to allow for the residual filament to run out after changing colors (see last photo on my Zekrom coin for my attempts at pausing during different layers).

Alternatively, you can set a 'Pause at Layer'

In Ultimaker-Cura:
Go to: 'Extensions' -> 'Post Processing' -> 'Modify G-Code'
'Add a Script'
Select 'Pause at Height'
Select 'Layer Number' in the first dropdown
Type in the layer you want it to pause at under 'Layer Number'
a. Pause at layer 6 to change from black to white
b. Add a second script and pause at layer 11 to change from white to red

In Prusa Slicer:
Go to the 'Printer Settings' tab
Select 'Pause Print G-code'
Enter the desired code: M25 ; pause print
...or if you are a novice like me - A pause can be inserted from the Preview window:
Drag the layer slider on the right to select the target layer
Right-click on the orange plus icon
Select 'Add pause print (M25 ; pause print)' A pause will be inserted before the selected layer is printed ....(or 'Add color change (M600)' if you have multiple extruders)
Insert a short message to be displayed on the printer LCD when the print is paused
ex: “Change to white now and resume printing”
Confirm the Pause by hitting 'OK'