"No country is fully independent" says nothing about whether Israel is properly classified as a colony. It's a platitude.

a right to exist

Another platitude. What do you mean by this? Israel's current actions are indefensible. Many of its past actions are indefensible. Its policy of neither recognizing a Palestinian state nor granting equal citizenship to Palestinians is indefensible. It must either fundamentally change or be replaced by a government worth supporting, like South Africa before it.

It certainly does not have a right to continue existing in its current form, no more than Nazi Germany did.