Xbox Design Lab was temporarily suspended last October while Microsoft worked on transitioning between console generations, but the custom controller service is back - allowing you to design your own Series X/S controller.
The relaunch was announced during Xbox's E3 follow-up showcase this evening, and the Xbox Design Lab website is now up and running. The customisation program allows you to pick colours for most external parts of the controller, including the "body, back case, D-pad, bumpers, triggers, thumbsticks, ABXY, View, Menu and Share buttons." The Xbox Wire blog post says there are 18 colours to choose from, including the colours of existing Xbox Series X/S controllers like Shock Blue and Pulse Red.
If you want to make it extra personal, you can also get your controller engraved with a Gamertag or custom message of up to 16 characters.