Cyanosis refers to a bluish skin color or that of mucus membranes that occurs mainly due to insufficient amount of oxygen in the blood. As per the cause of cyanosis, one may experience sudden shortness of breath along with other symptoms. If cyanosis has been caused due to long-term lung or heart problems, it would develop at a slow pace including the symptoms thereon. In people with dark skin, cyanosis can be easily detected in the mucus membranes, such as gums, lips and around the eyes, and in the nails. Medical tests performed by a doctor for diagnosing Cyanosis include arterial blood gas analysis, chest X-ray, blood oxygen saturation by pulse oximetry, complete blood count, and ECG.