This is my 5th day after extraction of upper molar. it is yellowish and i had a bad taste in my mouth. is this normal?

Very common: If you have food stuck in the socket, that could be the reason for the smell. You should rinse with warm salt water or mouthwash 3-4 times/day to keep food out of the socket. The condition is temporary and goes away in 7-10 days. Take care.

Healing: A bad taste is common after an extraction. Keep rinsing with warm salt water, especially after acting t keep the area clean and free form debris. Debris can cause the bad taste. If you do not have pain you are ok.

See your dentist: Sounds like you may have an infection. See your dentist to have it treated.

Yes: yes, the clot or site w/ take colors from red to white to even dark black to yellowish in your case. Think about what a scab looks like after a shower or you go swimming (it will be light color/yellowish). The mouth is a moist/open environment & the clot will take on different forms/colors. Bad taste = normal too, try licking a scab & it tastes bad too. This is totally normal. Keep it clean.