One of the most conclusive elements about the health of an orchid is the state of its roots. Therefore, we should always look first at them before any other part of the plant. Green roots with a hydrated texture indicate good health. Dry roots (gray to white) indicate lack of water. On the other hand, the dark onesusually indicate rot or death if they also have a fragile appearance.
It is common for all plants to have some fragments of roots that die without being a symptom of disease since the plant, as well as generating new shoots, eliminates those that are older. However, in a healthy plant should be strong roots, hydrated and a slight green color.
In some species, the observation of the roots can not be carried out in such detail since they do not necessarily use transparent containers or part of the roots are not aerial (dendrobidium, oncidium, cattleya, etc.).
In the image below we can see the roots of two Phalaenopsis. The one on the left has many aerial roots. Remember that these plants, in their natural habitat, the roots are aerial and are fixed to the branches of trees that serve as support but without parasitizing them. Therefore, they are comfortable producing roots that remain in the air. Its color is usually in shades of gray when they are not wet, they become green.
In the photo on the right we see some roots of an intense green color that indicates good state of the plant in general and good humidity level. If the roots were completely dry they would have a whitish color that would indicate the need for irrigation. If they are excessively dark and / or have lost consistency (volume) they are probably damaged by fungal or other attacks (usually due to waterlogging)