On the "Members Only Appearance" page, you can change the following:

• the accent colour
• the logo that appears in the menu on the left  (this is not your public site logo)
• your favicon/shortcut icon (the small icon that appears in your browser tab - this is not the one for your public site, though)
   

Note: public site logos and favicons are controlled in the Public Site Theme settings.
 

Where can I find these settings?

In the menu on the left, go to:
Settings & ​​​​​​Admin > Site Settings > Members Only Appearance

 

Changing the accent colour

The accent colour (or custom color) it used in tables and links. You can leave it as the default colour, or you can change it to a colour that matches your chorus/choir branding.
You can click the field to enter the colour code (if you know it), or use the colour gradient selector to choose the appropriate colour.

Changing the logo

By default, the logo your site will use is the choir genius logo. To change this, uncheck the "use default logo" checkbox. This will expand your options and display a field where you can upload a new image from your computer.
The path text field will display the path to your current custom logo if you are already using one.
Square images work best for your logo. That, or horizontal rectangles (wider than they are tall).
 

Changing the favicon / shortcut icon

By default, the favicon your site will use is the choir genius logo. To change this, uncheck the "use default shortcut icon" checkbox. This will expand your options and display a field where you can upload a new image from your computer.
The path text field will display the path to your current custom favicon if you are already using one.
Small square images work best. Make sure the image isn't too detailed - it will not display well in the small space available.

If you want something custom, but your logo won't work well, you can always try downloading free clipart of a music note.