Logos are like an attention grabber, they bring people's attention to the website and when you have a logo for something, you want people to look at that logo and think about your website, for example when i see the apple logo, i think of iphones, ipads, apple products.
i made my logo by putting in my own colors and things that are related to my website such as the moon, stars etc. I used dark colors such as purple, blue, black, white to make a nice cool night sky logo.