**Core Concept**
The yellowish discoloration of oral mucous membrane, skin, and sclera of the eye is a sign of a condition where there is an accumulation of a particular pigment or substance in the tissues. This condition is known as jaundice, which is a symptom of liver dysfunction or other underlying diseases.

**Why the Correct Answer is Right**
Jaundice occurs due to the breakdown of red blood cells, which releases bilirubin into the bloodstream. Normally, the liver conjugates bilirubin and excretes it into the bile. In cases of liver dysfunction or obstruction of bile flow, bilirubin accumulates in the blood and tissues, causing jaundice. The yellowish discoloration is due to the deposition of unconjugated bilirubin in the tissues, which gives the skin, mucous membranes, and sclera a characteristic yellowish hue.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the question as it does not describe a condition that causes yellowish discoloration of the oral mucous membrane, skin, and sclera.

**Option B:** This option is incorrect as it describes a condition that causes redness and warmth of the skin, but not yellowish discoloration.

**Option C:** This option is incorrect as it describes a condition that causes blue discoloration of the skin and mucous membranes, not yellowish discoloration.

**Why Each Wrong Option is Incorrect (continued)**
**Option D:** This option is incorrect as it describes a condition that causes redness and swelling of the skin, but not yellowish discoloration.

**Clinical Pearl / High-Yield Fact**
It is essential to differentiate between jaundice due to liver dysfunction and jaundice due to hemolytic anemia, as the treatment approaches are different. Hemolytic anemia can be caused by various conditions, including infections, autoimmune disorders, and genetic disorders.

**Correct Answer:** C. Carotenemia.