There are a number of ways to do inlays, and a number of alternatives. Some of the simpler options can be done using just Carbide Create, while others require additional software, possibly just Inkscape, or specialized commercial software such as Vectric Vcarve or Amazon Canvas.
First, the work-arounds:
- onlay — glue a second material to the stock, the cut it away: http://docs.carbide3d.com/tutorials/3-wood-sign/
- coloured stock — source two-colour material, or apply pigment and then remove a layer via sanding: http://docs.carbide3d.com/tutorials/tutorial-signs/weber-sign/
Carbide Create’s native facility with inlay is necessarily limited by the round endmills and their diameter for normal techniques, and its inability to flip designs. Symmetrical work can be done as shown in: Let’s make a coaster — basically one draws a symmetrical shape which will allow the endmill to get into all corners as discussed at: Inlay Work (Woodworking) — if the inlay and the stock material are the same thickness, then one doesn’t need to be able to flip one or the other, just cut both from the same side and then assemble.
One work-around for the inability to flip is to use the center of the stock for the origin (and place that at or near to the center of the machine), home / move the machine to that point, then reconfigure Grbl to reverse the X-axis, cut the part, then undo the reversal.