How do you remove the yellow colour of fish tank water?

It depends. Have you just started your tank? Have you recently changed your filter? If you just started your tank then you shouldn't worry too much. However if the color isn't coming out of the water after about a month or two you might want to consider changing 50% of your water. Also, if you bought gravel from Sears or just got gravel from rocks outside your house, the gravel might be dirty and you will have to start all over.