Installed Geany on a fresh Ubuntu machine & I realise it does't have much to offer as customization. Ran a quick
sudo apt-cache search geany yet nothing about the themes. I did an Internet search and then I realised the last time I customized Geany it was using template config files from Codebrainz Github page.
Just download the zip file according to your Geany version & extract the
.conf files to the ~/.config/geany/colorschemes folder. These should be now available under View > Editor > Color Schemes.
There's a vertical line representing the 72-character line break which you might also want to get rid of. Do it by disabling the Long line marker under Edit > Preferences > Editor > Display.
What is an IDE?
IDE stands for integrated development environment and that's a software which facilitates the work of software developers. An IDE consists of a source code editor, build tools and a debugger.
Update -- 25/09/2014
As JoKi states in the comment below, yes, indeed it's easier to pull updates via Git.
Use Git to pull the files on your machine and run
install.sh which copies the theme config files to the correct path.