Orchid roots should be firm to the touch. Healthy roots are often a whitish, grey, or greenish color. If they become brown or black that could be an indicator that there is a problem. Most Orchids are epiphytes and require planting in highly drainable course bark or similar. The roots need plenty of oxygen and regular moisture. Orchids can be overwatered though and will damage the roots and ultimately kill the plant if kept soggy as opposed to moist. Also the root tip can often be a different color than the rest of the roots when the plant is actively growing. This is normal and is often an indicator of growth stage and the flower color. Example: reddish to purple root tips on an Orchid will often have red to purple flowers and lighter colored root tips will be present on lighter colored flowers, etc. Roots are perishable and can be replaced with new roots given appropriate cultural care. If more than one third of the roots are dead it may be insufficient care. Many orchids are tropical and grown in greenhouses. When exposed to a new environment the roots can actually shrink and thin. It’s best to acclimate the more tropical species to a new environment.