I use high contrast mode on Windows 7 during the evenings as I usually work in low light conditions.
Most of my programs change the background to black on regular windows, and body text is yellow. However, Notepad++ does not change background or color of text. As I tend to put the screen on full brightness when in high contrast mode, NP++ tends to be blindingly bright.
I also typically have 10 to 20 tabs open. In high contrast mode, the active tab is blacked out and unreadable.
To access high contrast mode on WIndows 7, press left alt, left shift and print screen keys.
Other than this (and the fact that there's no left side tab navigator, only a right side navigator when the window is full of tabs), the program is fantastic. I use it all day, everyday.
If you change the theme which is selected from under the "Style Configurator" dialog window from under the Settings tab at the top you should be able to get the visibility the way you want. Only downside is that this will not automatically change based on your Windows settings and when you come back out of High Contrast mode you will need to change the setting again (unless your like me and want to always have a "terminal-ish" looking development window.