Custom Theme Main Background Color Bug

[Woshuojidan]

mangas have a bigger version of their cover in the background, just darkened so that the title can be read easily. this darkening is just a half-transparent layer of your main background color, which also gets lighter closer to the top of the screen.
However, if you set the alpha (transparency) value of your background color to anything below 1, the layer becomes completely clear, making the text that is on top hard to read.