I haven't been to all the greek isles (8 and counting..) but Zakynthos is by far my favorite of the ones I've seen. It's part of the Ionian islands/sea on the western side of the greek isles. The colors are completely out of this world. The blues we saw are some I've never seen before. What really made our trip was our Airbnb hosts. They took us in as if we were family. We would stay up late into the night under the pergola with them just chatting and laughing. You have to visit this place.
+ navaggio beach
+ navaggio beach look out
+ limniones (my favorite place on earth)