Based on Casper, the default theme for Ghost.
I've just made some small CSS changes, all to grayscale colors. Images automatically converted to grayscale, but you can see in colors if you put your mouse cursor over them.
##Installation
Copy it to your themes folder:
cd /path/to/ghost/content/themes
sudo git clone https://github.com/semeano/CasperGray.git
Restart Ghost and you should be able to see the theme option on general settings.
##Copyright & Licence
Copyright (c) 2014 Pedro Semeano - Released under The MIT License.
Copyright (c) 2014 Ghost Foundation - Released under The MIT License.
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.