If you are developer, you might want to change the template colors using LESS variables. You can find variables here:
These variables are commented and overrides via "Color" tab in template settings. If you uncomment these variables in the file, the variables will be in use.
Icons as images - how to change icons
You can use Category icon parameter in category settings to set up custom image icon. See analogue: Set up vector icons for categories.
Similar approach works for image icons. Use special class to set up custom icon. For instance: icon-deleted
You can change classes according to your requirements via LESS. Full list of icons can be found here: