I made my website where each page has a different color and I wanted to freeze header on all pages, but only problem was to make headers background in the same color as the page is, otherwise the page could look terrible when it is scrolled down. So, I had to place many shapes with different colors inside the header, hide them on load and with code which I implemented inside each page I wanted to show that specific shape. But it seems, that this dos not please me well. Because the similar shape can be seen in other pages, just refreshing the page, problem solves. But I cannot show to my customers, that sometimes page works, but sometimes do not.
You can see the example by labamuzika.lv link, check page koncerti and try to switch to another page.