Thanks for asking the query,
Dry mouth occurs due to various reasons , dehydration
, prolonged fever
, prolonged use of certain medications , salivary gland blockage ,disorders .
Brown colour of saliva can be due to bleeding gums which occurs due to gingivitis
I would suggest you to visit to Dentist
and get checkup done.
Get complete mouth scaling and polishing done .
Take lukewarm saline gargles , use antiseptic mouthwash gargles twice daily .
Take vitamin suplements .
Drink plenty of fluids
Hope this helps out.