One of the simplest text editors aroiund is Leafpad, it is fine for quick edits such as tweaking system files, but it does have its limitations when serious work is needed. For one, its search and replace function is pretty dodgy. It has no settings available of its self, it just takes on the system GTK scheme. It can't show mark-up of special file formats or folding of tag headers.
So what else is there for Linux? Two class editors I found are Geany and SciTE. Very customizable and they are both very capable as development environments.
To start off with them, you'll need to get a better color scheme going for each.
Geany has a few features better over SciTE. On the left-hand side is a panel which shows symbols (headers in a doc) and files - but you can remove files (I don't see the use in it) and show a file browser instead. These two panels make for a good experience, e.g. for working on html pages of a website. You can also setup auto completion of tags, and the like. If it had some auto text tools and it could almost take over from bluefish as html editor (except you won't have style properties dialogue).
To set a dark color scheme, first make an editable scheme file..
Then make whatever changes you need in this scheme file
The codes such as 0x000000 refer to a hex color code with 0x appended.
A value such as 0x000000;0xf0f0f0;false;false means: black fg, grey bg, not bold, not italic.
Then select the new scheme, View > Change Color Scheme (you need to select another scheme then your scheme again to see further changes).
Here's my dark theme. There may be some things missing.
And for the root color scheme, when opening files as super user or as root, to make the editor visibly different so that you are aware that super user priveleges are in use...
Enter the scheme text below and save, and then switch to the new scheme via View > Change color scheme.
Tip: change the shortcut for "Reload" from Ctrl-R to something a little harder to accidentally hit, such as Ctrl-Shift-D - otherwise you could lose a load of work if you forget to save the file for a while.
I got the following color scheme from the internet (pastebin) and it wasn't complete regarding some file types (no settings for xml and others). I've made colour adjustments.
In SciTE, Options > Open User Options File
copy and paste the scheme (and open a new file to see changes, as further changes may not reflect in the user options file).