My personal rule of thumb is that if the color adds significantly to the whole thrust of the image without being distracting, the I go with color. Otherwise I go with B&W (which is most of the time, for me.)
With this pair it's a close call for me. The color of the grasses gives a nice warmth to the color version, perhaps adding to the mood. But I don't feel that the picture is about color, so for the reasons John and Boudewijn have mentioned, I would go with the B&W.