Like all mucous membranes, your horse’s gums should be completely pink. Bright red gums can indicate endotoxemia; pale or white signifies anemia, shock, or even internal bleeding; yellow means liver disease; and blue generally means there is a lack of oxygen in the blood, usually due to lung disease.
Even gums that are mostly pink but have a dark red line at the gum-line of the incisor teeth can mean problems. Often called the “toxic line,” this can be a sign of toxemia, dehydration, and other abnormal circulatory states. However, redness around the gum line can also mean gingivitis.