I have created my Logs and added the 'Classifications', 'material type' and I am wondering how to add colours onto the logs to show for the different material types
In order to achieve this you'll need to (a) edit the picklists to (b) associate to some suitable image files (e.g., a solid colour you wish to display) and possibly (c) edit the template to access the appropriate picklist. It is possible you may have some of these steps in place already but you'll probably find this article on Communities really helpful as it gives an in depth explanation of what is involved.