Lord of The Rings: Fellowship of The Ring - Shot of the Ring
In Bag End, once Bilbo has left, and has left the ring on the doorstep inside, Frodo walks in and looks at the ring. From above, one shot of the ring shows it on a different surface than in Bag End (it is grey with grooves, not reddish with cracks). This shot was obviously taken from when the ring lays atop the table in the middle of the council of Elrond
This is not a slip-up. What they're doing is called "Foreshadowing." Foreshadowing is where they show, or tell about, a thing that is coming up later on in the story. By it showing the ring atop of the table in the middle of the council of Elrond, they're showing that later on in the movie, Frodo's going to have to make the choice to take the ring to be destroyed. They foreshadowed this because it was a crucial part in the movie in which the fellowhip is actually formed.
This is not a slip up! Having watched this film many times, if you look carefully, you will see that it is the floor tile, being shown at a different angle! The same crack is there, and it only looks like a bit is grey rather then red because the light is shining on it from a different angle, making it look grey!
Think to yourself: Why the hell would they change the floor tiles? This isn't gonna be a slip up, it is blatently a trick of the eyes, or something purposeful