Allergic Proctocolitis: This condition is a common cause of rectal bleeding in infants, often associated with the introduction of new foods or allergens. The presence of mucus with a slight blood tinge in the stool without other symptoms is consistent with this diagnosis.

Anal Fissure: A tear in the lining of the anus can cause blood and mucus in the stool, especially if the infant is constipated or has hard stools.
Gastroenteritis: Although the question specifies no other symptoms, mild cases of gastroenteritis can present with minimal symptoms aside from changes in stool.
Cow's Milk Protein Allergy: Similar to allergic proctocolitis, an allergy to cow's milk protein can cause blood and mucus in the stool of infants.

Intussusception: Although typically presents with more severe symptoms like abdominal pain and currant jelly stool, it's crucial to consider due to its potential for severe complications if missed.
Hirschsprung's Disease: A congenital condition affecting the colon that can lead to severe constipation and potentially blood and mucus in stool, though usually accompanied by other symptoms like failure to thrive.
Infectious Colitis: Certain bacterial infections can cause bloody stools and mucus, and while other symptoms might be expected, some cases can be subtle.

Juvenile Polyps: Benign growths in the colon that can cause rectal bleeding, though they are less common in infants.
Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause gastrointestinal bleeding, though it typically presents with more significant bleeding rather than just a tinge of blood.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis are rare in infants but can cause changes in stool, including blood and mucus.