How to change color and sidebar menu without using themes
There are 16 different departments so 16 different colors are needed. Create one theme for all of them. In your .css file create 16 classes and in each one set a custom background color. Like this

.dp—i{ background-color:#abcdef !important}


Now using preprocess functions, and based on the department add the css class to the page component. If it is a block use preprocess_block, if it is region use preprocess_region. By checking the department and adding approprite css class to the class array it will work