That is false, some are warm or hot
First, what is a nebula?
A nebula is a cloud of dust or different elements (remember, the Space is to a big extent empty)
A planetary Nebula is a kind of nebula that is specifically formed with ionized gas that was released and surrounds a red giant star.
Israel was first the holy land of Palestine and the Jews took over hope this helps
The sky is blue because blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.