|Table from this Reference|
Nasal fluid is normally produced by submucosal glands, seromucous glands, goblet cells, transsudation of blood plasma, mucosal tissue fluid, and tear fluid. The table shown is a description of what electrolytes are contained in normal nasal fluid produced by a normal, healthy human being.
Along with these electrolytes, nasal fluid also contains glycoproteins 10% by weight. Up to 50% of the glycoproteins present in nasal fluid is due to IgA. Smaller amounts of IgG and trace amounts of lipids are also present.
What all this means is that if nasal fluid dries out (ie, during very low humidity weather), the nasal fluid will turn yellow-brown just like water containing sugar. Classically, people would experience increased "boogers" and nasal crusting in the morning.
Beyond adding a room humidifier which will help, I also suggest using an oil-based nasal drop (I like ponaris) to help protect the nasal lining (just like using chapstick to help with dry, chapped lips).
Physiology and pathophysiology of respiratory mucosa of the nose and the paranasal sinuses. GMS Curr Top Otorhinolaryngol Head Neck Surg. 2010; 9: Doc07.