Other mistake: As the cloaked Warbird looks at the Enterprise, the registry number on the under side of the saucer is reversed.
Continuity mistake: Picard states that the energy beam appears to come from the deflector array, in later shots it is coming from the rear of the star drive section.
Continuity mistake: Just before Riker jumps through the portal with the female crew member he rescues, his phaser falls out of its holster, yet when he lands back in cargo bay 4 his phaser is right there in the holster.
Continuity mistake: In one scene on the planet, Riker's clone is lying under a table fixing something and Riker is sitting in a chair talking to him. There are two camera angles used. In one angle when the clone is talking and a body double is sitting in the chair he is facing directly towards the table but in the other camera angle where you can only see Riker, the chair is at an angle facing towards where his clone is lying on the floor.
Revealing mistake: When Frank Hollander visits Eli in jail, you can see a dummy in the cell.
Continuity mistake: Data is driving a pair of brown horses pulling an enclosed carriage. You can see the side of the carriage as it comes around the corner. Next shot, when they climb aboard, it is open-sided. (00:17:40)
Continuity mistake: In the opening scene, Riker's rank pips are diagonal on his collar. Then in Worf's quarters, the pips are level as they should be.
Continuity mistake: William Riker is playing cards with La Forge and Worf. The camera is focusing on Riker and there is no 4th chair. When Tom Riker enters, William says "Why don't you join us" and now removes his trombone from the 4th chair which has suddenly appeared. (00:31:25)
Continuity mistake: Data's insignia pips are backwards in the first scene as he is talking to Picard on the bridge.
Revealing mistake: In the cargo bay, as Riker stands alone, through the whole scene where a case is about to hit him, you can tell it's a stuntman with a bad wig.
Continuity mistake: As Geordi talks to Ms. Rogers, Riker is walking in the background by some containers and a crewman in blue. After a cut to Ms. Rogers, Riker is suddenly alone with a data pad.
Descent (1) - S6-E26
Revealing mistake: In the hand-to-hand with the Borg soldier, Data's stunt double is easily identifiable.
Continuity mistake: When Deanna is trying to seduce Riker, she scratches him and there are three deep scratches on his neck. Later, when Doctor Crusher treats him, one of the scratches is now on his cheek, and only two are on his neck.
Other mistake: When Ro Laren enters the Jeffries tube, she makes a sudden shift to her right (our left) as she begins crawling; she was trying to avoid the camera.
Revealing mistake: When the first villain hits Worf with the chair, just as Alexander is yelling "look out", you can tell it is a stunt double.
Chosen answer: The uniform does indeed change colour. It may be due to the need for a green screen in part, or perhaps some lighting altering our perception. That being said, it certainly looks green at the start, blue thereafter.
The show has been done in HD now and not sure if they fix this problem.
Dan23