Leg colour should be green. There is a wide permitted colour range from willow green to lizard green. The photos below should help you to understand what is permitted and what is outside the breed standard.
Yellow, white, very pale yellow, slate, blue, black and any feather on the legs is not permitted. The photos below are outside the standard and are a serious fault.
The ideal colour is willow green and that used to be the standard. However, willow green is very hard to achieve in the blacks and the browns and so the standard was recently relaxed to allow a darker green known as lizard green to be permitted. The photos below indicate the various shades of acceptable willow green.
The three photos below are considered to be right on the bounds of acceptable and in the opinion of some outside the acceptable boundary.
The photos below show the darker now permissible lizard green