After I finished these smaller coaster (3 1/4 inches in diameter) with an F hook, I remembered that the larger diameter coasters (4 inches) with the same pattern were made with a three size larger hook, an I hook.  The tighter stitch makes for a less smooth a trim circle.

 Here I tried a set in marl,  trimmed

 with with solid green, the best looking solid color, and made into a set with one of each of the solid colors trimmed with the Christmas marl.  Of these the white with marl looks best when viewed live.

 These 4 1/4 inch marls are done with three inner circle of double crochet, followed by a row of single crochet, and ended with a row of double crochet.