The 'traffic light' system was introduced in Scotland last month, allowing holidaymakers to jet abroad for the first time in months.
People are now able to travel to "green list" countries without having to quarantine, provided they take one post-arrival test.
However, most countries on this list are closed to UK travellers, while others will only let in those who are fully vaccinated.
Nicola Sturgeon has repeatedly urged caution over foreign holidays, asking Scots to 'think seriously about whether they really need to travel abroad this summer'.
With the list constantly changing, airlines have been forced to update their policies spelling disaster for those with flights and hotels booked.
Here are the latest updates for easyJet, Tui, Jet2 and Ryanair:
easyJet
EasyJet has cancelled flights and changed plans as they adjust their schedule to meet demand.
A number of customers have had their holiday plans scrapped as a result of the changes, although the airline has said that everyone will be entitled to a full refund.
EasyJet issued their latest statement on upcoming flights after many had bookings cancelled to countries such as Spain and Greece in June.
The statement read: "We want to fly as many customers on as many flights as possible this summer, however as all airlines have been doing throughout the pandemic, we continue to adjust our flying schedule based on the restrictions put in place by Governments to ensure our flying programme best matches demand."
The spokesman added that easyJet is "communicating with any customers impacted by a cancelled flight" in order to ensure they are aware of the options open to them, which include a full refund.
They said: "We are providing customers with more flexibility than ever before with our Protection Promise which enables customers to change their flights fee-free up to two hours before their flight if they are no longer able to travel.
"We have consistently urged the UK Government to increase the number of countries on the Green list and have kept our aircraft and crews in flight-ready mode so we have the ability to ramp up to 90% of our fleet by peak summer so we are ready and able to ramp up.
TUI
TUI has cancelled more flights and holidays to a number of destinations this summer.
The travel group has axed trips to amber and red-listed countries until next month.
TUI recently scrapped trips to Turkey and several other destinations because of restrictions on travel.
They said they had to "unfortunately cancel all holidays to the following red and amber destinations" up to and including June 13.
Aruba, Croatia, Cyprus, Greece - Crete (Chania), Halkidiki, Kefalonia, Preveza, Samos, Santorini, Skiathos, Thassos, Zante - Italy, Jamaica, Spain - mainland Spain, Formentera, Mallorca, Ibiza, Menorca, and La Palma.
All TUI Lakes and Mountains holidays are cancelled up to and including June 13, while trips to Bulgaria, Cape Verde, Costa Rica, Dominican Republic, Egypt, Mexico, Morocco, Tunisia and Turkey have been axed until June 27.
Jet2
Jet2 is not starting their holiday and flight programme until June 24.
They said: "We’re taking the time to get everything ready at our airports, onboard our planes and in our resorts to give you the safest and smoothest holiday experience possible.
"Our teams both in the UK and overseas can’t wait to welcome you back – we’re excited to give you the holiday you deserve.
"If your booking is affected in any way, we’ll be in touch with you as soon as we can. We kindly ask you to hold off from contacting us and wait for us to get in touch with more details.
"Please visit our website 14 days before you’re due to depart, when we’ll have all the latest official information.
"Between now and then, there’s no need to take any action – and we’d recommend that you don’t start arranging things like Covid-19 tests until closer to your time of travel, as travel requirements both here and abroad can change."
Ryanair
Ryanair has continued to operate some flights throughout the pandemic - on mainly domestic routes, for essential travel.
The low-cost airline is now flying to green and amber list countries, but is offering passengers more flexibility.
Regarding new bookings for the summer, the airline has a statement on its website reading: "We know your plans may change, so we've dropped our flight change fees for all new bookings made before 30 June 2021, for travel before 31 October 2021.
"You can now make up to two flight changes for travel by 31 October 2021. This gives you complete flexibility and peace of mind.
"Our Zero Change Fee promo is applicable for bookings made after 10 June 2020.
"Flight changes must take place at least 7 days before the original scheduled departure dates to avail of promo. Fare and product price difference may apply."
