Wallpaper Alpha (or WAlpha, the name you'll find it in Cydia) is a modification that allows you to adjust the transparency of your wallpaper, so it look more or less dark. Eliminates other transparencies such as Spotlight or the battery charge (zero transparency in this case). It is best you do not need Winterboard to apply, because as you know Winterboard consume enough resources and I recommend it.
You can download it for free on Cydia.
The repo'll find Modmyi.
You need to have done the jailbreak.