after rooting the start up sound can be found at /system/media/ I can't tell you what the file is named because iv allready deleted it (it was obvious) Its also safe to delete the boot_logo and shutdown_logo found in the same location it gets replaced with the stock android logo The super su app has...

I don’t like white backgrounds on my menus, phone dialler, messaging app etc… There’s a new theming engine called substratum.. while I was trying out dark themes I found allot of them were changing the system icons so It might be something you’d like to check out? Video example of themes Substratum ...