I am looking for a note taking app with white text on a black background that works with iCloud. Apps for Mac and/or iOS will work. Any recommendation?
You should expand your requirement to iCloud and Dropbox for following reasons.
I have tried over a dozen note taking apps that syncs over the cloud. The app that I keep going back to is Elements (http://www.secondgearsoftware.com/elements/). It has very clean yet functional UI and frigging fast.
I do have few wish list items though: (1) tagging and/or support for moving notes to different folder, (2) hide certain Dropbox folders (I linked to the root folder), (3) default font setting (Museo Sans is very pleasant but may not be for everyone), and (4) Markdown keyboard (it fully supports Markdown but I don't remember all the syntax).
There's actually a very beautiful app called iA Writer that has a focus typing mode. Though normally supposed to be used for actual full-blown blogs and such, there's no reason you couldn't go and use it for notes.
This is the description of the iCloud feature from http://iawriter.com:
iA Writer for Mac can be downloaded here.