[going hot]

how do you get the pattern on the glass, or is that an insert or protective cap under the flip ups.

[Charles Martel]

That’s a Killflash (threaded in like a camera lens filter). DuraCoat in an airbrush, using a digital camo stencil kit.

[MasterGunner01]

“...how do you get the pattern on the glass, or is that an insert or protective cap under the flip ups.”

That gizmo is called a Killflash filter. It resembles a honeycomb and installs in the objective end of the rifle scope. It is specifically designed yo prevent light reflections off the optics. A reflection off the optics at the wrong time and place can give away the shooter's position.