Jason Reitman worked hard to bring back the "original-colour slime" for 'Ghostbusters: Afterlife'.

The filmmaker - whose father Ivan directed the first two movies in the beloved franchise - is at the helm of the upcoming sequel, and he admitted it was a tall task recreating the right "green" from the 1984 classic.

He told Empire magazine: "The slime colour has changed from film to film, and I wanted original-colour slime. We kept on zeroing in on, 'That's too green. That's not viscous enough'.

"One day, they had two different vats and there was a huge argument over which one was right.

"I said, 'Dad, can you come over here?' And my dad just went over and pointed to a bucket and said, 'That's slime.' "

Ivan joked: "I think my greatest argument was that there should have been more goop."

Beyond the colour of the slime, another challenge for Jason - even beyond following in his father's footsteps - was finding the DNA of 'Ghostbusters', which proved difficult to pin down.

He explained: "I think it depends on the age you were when you saw the original, because for a lot of people, it was a horror film - it's the first scary film they ever saw.

"They think about the terror dogs, they think about Gozer and they think about the original Slimer, who was just horrifying.

"And then for a whole other generation, it's a straight-up comedy starring some of the funniest human beings that were alive at the time: Bill Murray, Dan Aykroyd, Rick Moranis, Harold Ramis.

"And then for others, it's a science-fiction film done my puppeteers and science-fiction visionaries working at the top of their game.

"So, the real balancing act is finding a movie that is within the language of the original '84 film that both scares you and makes you laugh."

For Ivan, the original film - and now its upcoming sequel - have a certain "level of sincerity" which carries the story amid the madness.

He added: "There's a level of sincerity both in the '84 film and certainly in this one, that makes all these fantastical, humorous, goofy things somehow believable. You get emotionally involved in the storytelling. It's what I love about 'Afterlife' so much."