Yes a few travel companies tried this on last year.
When the "Red" Amber" Green" system was first introduced you were not (and still are not) prevented from travelling to countries in any category. It's what you have to do upon return where the differences lie. At that time, people returning from "Amber" countries (which mine was) had to isolate at home for ten days. This was clearly impossible for many people and undesirable anyway.
My tour operator suggested that because both my flight and accommodation were operating as planned, if I should cancel I would forfeit my money. However, what they did not seem to realise was that to all "Red" and almost all "Amber" destinations the Foreign Office had advised against all but essential travel. This meant that virtually all travel insurance policies did not provide cover. Since almost all tour operators make a condition of booking that travellers have adequate travel insurance, they were therefore insisting (on pain of forfeiture of payment) that their customers travelled not only against FO advice, but also without the insurance cover which they insisted on.
I think that stance lasted no more than a few days. ABTA and ATOL both decreed that where government regulations effectively prevent you travelling, that a full refund is due. You should note that this only applies to package holidays where all elements of it are booked with one provider.