Why is my tongue yellowish everyday?

Bacteria or thrush: Bacteria can grow on the surace of the tongue creating a coating. This coating is then coloered by what we eat and drink. Another possiblity is thursh (a fungus infection). Gently brush your tongue with your toothbrush twice a day when you brush your teeth. If it doesn't go away in 7-10 days and/or it leaves behind a bleeding suraface then see your dentist.

Use a tongue scraper: Your tongue has small bumps on it called papillae. When these papillae get filled with bacteria they can become swollen and discolored turning either white, yellow or sometimes black. They can also become elongated causing what is called white hairy tongue or black hairy tongue. This is also a major cause of bad breath. Try scraping your tongue with an oolitt tongue scraper as far back as you can.