Depending of your email client, you might have noticed that your emails look the same (eg. Apple Mail app) or different (eg. Outlook, Gmail) when your device is in Dark Mode. The reason for this is that email clients handle dark mode rendering differently, either they:
do not change the colors (email looks the same on Dark Mode) - e.g. Apple Mail
partial color invert (light background colors will be changed but not dark ones) - e.g. Outlook.com
full color invert (force-inverts all colors) - e.g. Gmail App iOS.
Images are not always inverted and dark logos can be hard to see in Dark Mode. Some email clients make it impossible to overwrite their Dark Mode. We suggest therefore to add a white shadow to your dark logos or images so they are always readable in Dark Mode.
More about this topic:
Why are the colors in my email different in Dark Mode?