The UK's traffic light rating system for Covid-related travel guidelines is updated regularly as the pandemic progresses and evolves. As this chart using government information shows, the number of countries and territories without a travel warning in place is very limited, despite the seven countries that will be added on Aug 8. They are Austria, Germany, Latvia, Norway, Romania, Slovakia and Slovenia.
Other main destinations (albeit far flung) on the green list are Australia, New Zealand and Israel, with Bulgaria being a closer option. However, the ratings and associated rules apply only to people returning from these countries. Travelers should inform themselves of the rules currently in place for entering the country they intend to visit - Australia, for example, has closed its borders completely, making the UK's green status for the country only relevant for people already in Australia.
Equally, while the 'amber' countries may not apply such extensive measures for returnees to the UK as for those from 'red' rated locations, both carry a "You should not travel to these countries or territories" label. Full guidance can be found on the GOV.UK.