You can create you own theme, changing the color scheme as well as the logo.
Please refer to http://knowage.readthedocs.io/en/6.1.1/admin/theme/ to know how to override the default theme with a different one.
To understand how to create a new one, have a look at https://github.com/KnowageLabs/Knowage-Server/tree/master/themes, where you can find an example of custom theme (namely FIWARE). You can use that as base to start.