If not you better skip this. Below loads of Different Caspian Gulls of all ages, ive had fun going through hundreds of em.
Now onto a few Yellow Legged Gulls
Just to confuse matters further a picture of a Northern Herring Gull (argentatus) The birds are bigger, with a dark mantle, the same color as a YLG, dirty head.
Lastly a 1st winter Lesser Black backed gull.
Gulls are great but very tricky, the saying goes if you don't make mistakes looking through gulls then your no expert ;-)