The most critical element is a "Stormtrooper White" or "Bright White" Cerakote coating on the frame or slide, often paired with "Armor Black" or "Graphite Black" for contrast.
Some choose a "distressed" or "battleworn" finish to make the firearm look like it has survived several skirmishes in the Outer Rim.
Laser-stippled grip patterns can be designed to resemble the textures of Stormtrooper armor or E-11 blaster grips. Visual Examples
Custom engraving or stenciling of the Imperial Cog symbol on the grip, slide, or backplate.