A deep green sill with a squared return at the open end, set into a library nook. Painting rather than staining let the sill match the room's joinery exactly instead of approximately.

Painted sills are sprayed in 2K polyurethane over a paint-grade substrate, which is the most moisture- and chemical-resistant finish system offered. Any of 373 Sherwin-Williams colours can be specified, in matte, satin or semi-gloss. Matte hides prep and touch-ups best, semi-gloss is the most washable, and satin sits between the two — the usual choice where a sill has to match existing trim exactly.
A study or reading nook sill is frequently used as a shelf, so depth and the front edge take priority over ornament. Whatever the room, the sill is cut to your opening rather than trimmed to fit on site — length, depth, horn projection and corner treatment are all set before it is machined.
Measure jamb to jamb, then the depth from the window frame to where you want the front edge to land, and the horn length past each side if the sill returns into the wall. The configurator draws the piece live as you enter dimensions and produces a dimensioned spec sheet you can hand to an installer. See the measuring guide for the full method, or compare wood against solid surface before choosing.
This image is a rendering, shown to illustrate materials and proportions available through the configurator.