I notice that the header of this site (you can see it for yourself) only has plain blue. Why doesn't it contain some drawing?
Some other headers of other Stack Exchange sites:
Disclaimer: I have considered to ask this question on the meta of SE, or the meta of this site. However, since I don't know much about UX, I think this is intended. Therefore, there is some thing about the UX, and it will be best to ask here.