IMHO, green patio carpet looks "right" -- except if you intend to build a realistic layout with lots of attention to detail. That carpeting is readily available, affordable, easy to install, and easy to clean with a mini-vac.
I prepared the four sections of my 15x19 feet L-shaped layout with carpet adhesive, laid the carpeting in place, smoothed it out, wrapped it over the edges, trimmed it to fit, and stapled it to the underside of the platforms. It's "on there" permanently. By intention, I didn't install streets, curbs, and sidewalks on my 1950s-era traditional layout. The "edge to edge grass" looks OK to me.
I installed Lionel O42 tubular track and switches atop the carpeting (without ballast), then put buildings and accessories in place. Perfect. BTW, if you want a Christmas-theme layout, patio carpeting is available in WHITE (or a "salt & pepper" color - which looks like urban snow with accumulated soot). Those colors may require a special order via Lowe's.
Note 1: I placed lots of O-scale figures on my layout. They won't stand up on the carpeting, so I applied a drop of glue to the base of each figure to hold them upright in place.
Note 2: Like most hobbyists, I run the wiring for track, switches, action accessories, and lighted buildings underneath the platforms and then drill 3/8th-inch holes to bring wires to the surface of the carpeting for hook-ups where needed. To avoid ragged edges or unravelling of the carpeting, after drilling I place a 3/8 brass grommet at each hole with a drop of glue. If the layout is changed, the grommets can be pried up, and the carpet fibers may re-cover the hole.
Pix of my layout attached for reference.
Mike Mottler LCCA 12394