You should be able to repeat this issue by changing the body bg color #262626.
I don’t have Jevelin loaded as active theme because of this issue. I am frustrated that you have to ask me to show you the issue. I clearly described the problem and gave you a screen capture. I cannot show Jevelin theme on http://www.lightpaintingstick.com any longer because it is uninstalled. I will put it on another domain in the future.
That works for headers with bg color #262626. But the transparent headers do not work.
Here is a pciture.
The website is http://www.lightpaintingstick.com
no transparency for the header text when body bg color assigned #333333