Hi and
I would not add another color rock or pebble or a different surface since you already have three "surfaces ".. The flat stone..the tiny path /sand, and the pebbles like the ones you circled. More would make the eye jump around and lose the point of the path which is to lead the eye to the entrance door as well as be functional for the feet!
Instead, since the eye is being led.....give it something along the way to admire. What about s bench in the area you circled? Curved to follow the shape of the pebbled area. A pretty browned red to match the earth colors you already have or a dark dark blue...perhaps a birdbath..or a pot here and there andyou can hang out what is planted .Let the hardscape be what it is and add interest.
