The mum-of-one first set foot in the Buchanan Street branch of the salon 22 years ago, when she was just 15-years-old.
After begging for a job as a stylist at the salon, which brought cutting edge London style to Glasgow, she worked her way up to become the owner, along with her husband Wil.
Six years on, and as the branch marks its 35th anniversary, Shannon and Wil are celebrating the salon's achievements.
The team sees around 300 customers a week - and around half of those clients come for colour treatments, which the salon specialises in.
"Rainbow Rooms has definitely been life changing for me," says 37-year-old Shannon as she sits in the busy salon.
"It's in my blood. From 15 to this stage, it's brought me a career, a whole load of friends and it's brought me a husband."
Shannon, from Newton Mearns, was inspired to be a hairdresser after discovering how glamorous the Glasgow salon was.
The Buchanan Street site was launched in 1979 by Alan and Linda Stewart, below, from Glasgow, who now manage the Rainbow Rooms International brand.
It was their first salon, before they grew the brand to 12 branches across Scotland, and two training academies.
Shannon says: "I was walking by one day and I was inspired by the place and all the glamorous women who worked there.
"There was nothing available at the time but I just kept going until someone eventually said: 'Give her a brush'.
"I worked my way up through all the ranks, winning a lot of individual awards."
Shannon then decided to take a different route and "give something back" by managing people.
"I trained in the Rainbow Rooms in Clarkston and eventually started running it," she says.
"Then I was offered the Buchanan Street franchise, which is just the Holy Grail. It's the hub of the Rainbow Rooms."
Shannon and Wil, who was manager of the Stirling branch, have been married for six years and have a 20-month-old son, Ace Rock.
Wil, 44, moved to Glasgow from England to join the company in 1996.
"I moved up because the pull of the brand was so strong," he says.
"The company had a reputation in the industry.
"Alan brought what was then London hairdressing to Glasgow."
Wil began in the Royal Exchange Square salon, before moving to Great Western Road and then opened his first salon, which the couple still own, in Stirling.
He said the brand "still has Glaswegian heritage".
"Every single client needs to leave with a six star experience so they go out and talk to friends," he says.
The pair are proud to employ the UK Stylist of the Year.
Joy McQuillan won the accolade at the Hairdressing Journal's British Hairdressing Business Awards last year.
Shannon and Wil say the success of the salon's 35 year history is down to the "unbelievable team".
"We feel very lucky and blessed," says Shannon. "We've picked up so many awards.
"Clients come again and again."
Wil says their proudest moment was taking over the franchise.
"The take off was incredible," says Wil. "It had no direction, because they were waiting for a team to come in and say: 'We're going this way'.
"We doubled our turnover in the first year. It went stratospheric."
The couple say there is "no doubt" they will be part of the Rainbow Rooms team in the next 35 years...but they now want to hand the reins on to fresh talent.
Will says: "Alan and Linda noticed our talent and gave us opportunities
"We'd love to do exactly the same and hand over to the next generation."
Shannon adds: "It's important to see my youngsters evolve to the best."
Founder of Rainbow Rooms Alan says he "couldn't be more pleased" with the success of the Buchanan Street branch.
He adds: "When I opened it in 1979, I wanted it to be Scotland's first destination salon.
"I never imagined that we would still be here 35 years and 12 salons later.
"Wil and Shannon have done a great job of managing the Buchanan Street salon and I couldn't think of anyone better to do so."