New Rangers manager Pedro Caixinha has banned his players from wearing green boots.
The Portuguese has set out his rules for the new season after giving his squad an overhaul.
Rangers have already returned to competitive action, beating Progres Niederkorn in the Europa League on Thursday.
And Caixinha’s zero-tolerance approach has been revealed, reports the Daily Record.
Caixinha explained: “From today, no one will wear boots of that colour because it is the colour of Celtic.
“The slogan ‘We are the People’ will be stamped on the walls for both our players and opponents to feel the strength of Rangers.”
He recalled: “The Rangers fans are full of hope, the Celtic fans are upbeat and excited and that’s normal because they have won six titles in a row.
“Only once have I been bothered. In the centre of the city, a drunk Celtic fan upset me, but it was nothing.
“The centre of Glasgow is beautiful like the rest of the city.”
Caixinha used to have scouting links with Celtic when he was in his homeland as a coach.
And he revealed he even helped them sign one of their star players seven years ago when they dipped into the South Korean market to snap up Ki Sung-yueng.
Caixinha said: “I was in Glasgow for my UEFA Pro Licence and I met Helena Costa, who was already working for Celtic.
“I spoke to her about Celtic setting up a base in the Iberian Peninsula and even recommended a player to them – Ki Sung-yueng, which they signed and is now at Swansea City.”
Caixinha, speaking in online newspaper Observador, famously was a Portuguese bull-fighter for years and he revealed how one of the creatures left a lasting mark on him that remains to this day.
He said: “I have many good friends in football. But my real friends are the ones I met with the bulls. They will remain my friends forever.
“I had my first bull at seven years old and at 14 I had to make a choice and I chose football.
“But I was part of the Montemor Forcados group for 12 years. I have fought 100 bulls. I travelled with them to France, Spain and Macau.
“Every bull is a new experience. It can be like football. We have to analyse the behaviour of the bull. It’s still about tactics.
“I have had some unpleasant experiences. It’s gone wrong sometimes. You see the scar on my chin…that one was a mistake – the bull opened up a second mouth on me!
“I’ve never been knocked out, but I admit that one left me dazed.”