You need some two color engraving acrylic, with a red cap color and white core color. Then you just engrave the design. Here’s where to buy some.
This thread has some discussion on settings to start with. Always do small tests to make sure the appearance is coming out how you’d like before running a full design and potentially wasting expensive material.
P.S. My experience with laser engraving red on white with a Glowforge is that the air assist fan will blow some of the vaporized red plastic into the white engraving, so you’ll need to run a second pass (which can be done at lower power and lower LPI) to clean it up and get a crisp white engrave area.