Unfortunately you can not change the text color of the navigation/menu box on the left with "Customize Your Account's Branding".

For example: our brand color is a dark green and box.com automatically determine the text color to a dark grey. It looks very dark and weird now, there is any contrast and it is not very reader friendly.

The ideal thing here would be to make the text white, such as on the navigation/menu box from the admin console page, a dark gray background with white text.

It would be very helpful to add another option in the "Customize Your Account's Branding" where the admin could choose or customize the text color themselves.