Editing table layout in PowerPoint slide master

I am creating a new PowerPoint template with an unique background. None of
the preset tables in PowerPoint look good with my background, so I want to
change the default look of the table in the Slide Master to a table format
that I have created.

While I know how to set one of the preset table styles as the default (right
click chosen style, Set as Default), I can't figure out how to add my own
table template to the Table Styles. Any ideas for adding an unique table
style to the Slide Master?