There is a problem with selecting the color of the logo so that it meets the contrast requirements of WCAG 2.1 in both dark mode and light mode.
The rocketchat logo contrasts well with both the new login screen in rocket.chat 5.4.X. On the other hand, a logo in this color is rare.
That’s why I suggest adding a separate logo option for the light and dark theme.
For example, Microsoft Azure has options to add two different logos - one for dark theme and one for light.
This is believed to be one of the required elements for implementing a true dark mode in RC 6.X.