Interesting fact. It Isn't bigger!
This is a well known optical illusion that dates back hundreds of years. It's all in your head, it seems bigger because your brain perceives size as something that is relative.
This is an effect called perspective distortion and is will understood and used in photography. Phil Plait's Blog (A.K.A - The Bad Astronomer) also writes on this matter and would be worth reading.
Consider the below picture:
As the focal length of a lens gets longer the difference in relative size of foreground and background objects becomes more pronounced. Your brain then interprets this and respectively the moon seems huge!
But why does it look yellowish?
It appears yellow sometimes because our atmosphere blocks and stretches certain wavelengths. So when the moon is low in the sky, it has to pass through the most atmosphere to get to you, stretching and distorting the light through the yellows and oranges.