These are customizable flaps with digits for Split Flap Clock by The_Wrench_DIY (https://www.thingiverse.com/thing:5964202)
You can print it as is or customize (scad file is available)
You can use different filament color for middle layers, or print in one color and then paint it with a marker.
The thickness is 1.2 mm by default, so if you print in 0.2 mm layers, it will be 2 layers of one color, two layers of a different color for digits, and then another 2 layers of the first color.