Magpies slumped to a 5-1 defeat at Selhurst Park on Saturday, which left them struggling in 19th position on the Premier League table.
In the wake of yet another demoralising display, 26-year-old Colback told the club's official website: "We had a game plan and in the first 15-20 minutes it worked perfectly. We got the goal and you could see they were rattled.
"But we let them straight back in, then I made a mistake for the second goal and that put us on the back foot again. After that it was pretty embarrassing, really.
"Maybe we're not strong enough character-wise. It seems as if as soon as things go bad, it goes really bad.
"We had that last year and probably the year before as well. It's something that's hanging over the team that we need to get rid of.
"We had shown signs of improvement but the Leicester game and this one have really set us back quite a lot."