This page lets you change what your portal looks like. The fields are mostly self-explanatory but here's a brief overview of where each item appears:
Logo: Your main logo, displayed in the top left hand corner of your portal. Suggested dimensions at least 80 pixels wide and 40 pixels high. PNG/JPG/SVG supported.
Square Logo: Used in certain areas of the site where the full logo can't be displayed. Suggested dimensions at least 40x40 pixels. PNG/JPG/SVG supported.
Favicon: A small image to identify your site in browser tabs (see example below). 16x16 pixels. PNG/SVG/ICO supported.
Primary colour: Used in headings, borders etc
Secondary colour: Used mostly in backgrounds
The easiest way to see where your primary and secondary colours are used is by setting them first and then viewing a few pages of your portal.