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.

geany-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.

geany-vertical-line-marker

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.

$ cd ~ && git clone https://github.com/codebrainz/geany-themes.git $ geany-themes/install.sh

Use Git to pull the files on your machine and run install.sh which copies the theme config files to the correct path.