Please explain the colors on a See-All sight glass. This is a new sight glass. The sticker on the side of it has the color green with Dry typed over it and the color yellow with wet typed over it. Inside the sight glass in the middle there is a 1/4" diameter material.

Does the thing in the middle turn to a green color if there is not enough refrigerant and turn yellow if refrigerant goes over it? If it turns yellow is this what is meant by charging to a clear sight glass? Do you use the colors to check refrigerant charge?