Rope, like hair, is difficult to recreate with paint because of its depth of detail. Here's a suggestion for sisal/hemp rope:
Use a base coat of medium saturation low chroma green, such as a "green" shade of olive drab. Glaze with slightly transparent yellow-tan, then wash with burnt umber. Finally, highlight by drybrushing with a very gray off-white. That gives four levels of color depth, and, as long as you keep everything in the green/yellow part of the spectrum, its pretty effective.
Phil