White mucus sputum is most often seen in the remission phase of simple bronchitis, early pneumonia, bronchial asthma and alveolar cell carcinoma. If white mucus sputum is drawn into a filamentous form, it is often a Candida albicans infection.
Yellow sputum is more often seen in purulent infections of the respiratory tract, such as Staphylococcus aureus pneumonia and purulent bronchitis. If greyish-yellow mucous sputum is present it is often an infection with Aspergillus fumigatus and yellowish-green sputum is often an infection with Pseudomonas aeruginosa.