White color of teeth is becoz of our tooth first layer which is enamel. If your teeth reflect yellowish color that means your teeth enamel is thin and inner layer dentin color is visible. But if your teeth has brownish color that means stains are there which can be removed by scaling ( professional cleaning of teeth).
Bad smell from mouth after having food is due to acid which is produced from the decay of the food you had. after having food pH of your mouth decreases. you should always rinse your mouth with water aftr food and you can take some chewing gums like orbit aftr meals. but definitely you should go for scaling and polishing once in a year and regular dental checkup. follow oral hygiene measures like twice brushing daily and flossing at home.