A buckskin is a cream gene added to a bay horse. Buckskins can range in shade from a very light "buttermilk" shade to a deep golden colour. All of them have a gold tint to their coats. Buckskins CAN have dorsal stripes, but the majority do not.
A dun is a dun gene added to a bay horse. Duns are generally a dingier golden shade. Does that make sense? Kind of like if you took a shiny golden buckskin and covered them in a thin layer of dirt to make them look a bit more dull. Duns also have "dun factor" markings. These include dorsal stripes, leg barring, and shoulder barring.
Then there's a colour called Dunskin. It is a buckskin with the dun gene. Dun is just a gene that can affect any colour. Most common is grulla (dun on black) and a red dun (dun on chestnut).
I'll go find pictures.
Sixlets, buckskins CAN have dorsals stripes.