These are the colors the laser can see
Black is used for engraving (R0,G0,B0) Please note that shades of gray will give a gradient for engraving and can be one way to vary the darkness of the engraving.
Red is used for cutting (R255,G0,B0)
Blue and Green are used for secondary operations (R0,G0,B255 or R0,G255,B0)
Usually you will want to use blue or green for cutting parts with internal geometry. That way it can be set to cut everything on the inside before the outside.
For cut lines you will want the lineweight to be set to the following:
AutoCAD → 0.00mm or 0.00in
Inkscape → 0.5pt or less (this will be called stroke)
Adobe Illustrator → 0.001pt (this will be called stroke)