A guest with dark mode switched on may see your campaign with inverted colours, a logo that has vanished into a black background, or text you did not choose. This is decided by their device and email app, not by Bookboost, so you cannot switch it off for them. What you can do is design so it holds up either way, and check it before you send.
Two different things called dark mode
These are easy to confuse, and only one of them affects your guests.
The dark mode toggle in Bookboost is a preview feature in the campaign builder. It shows you how the email might look on a dark background. Turning it on or off changes nothing about how the email is delivered.
Dark mode on the guest's device is the real one. Their phone or email app decides how your message is rendered when they open it.
So a guest with dark mode active can receive your campaign in a dark theme even though you never enabled anything.
How to see the dark mode preview
The toggle is inside the editor's own preview, not on the campaign's Preview button, which is why it is easy to miss.
Open the campaign, go to 2. Content, and select the Editor mode.
Find the small dark toolbar at the bottom left of the canvas, holding undo and redo. Click the eye icon on it.
The preview opens with its own bar across the top: a desktop, tablet and mobile icon, a width dropdown showing something like 1280px, and a sun icon at the right.
Click the sun. It becomes a moon and the preview switches to dark. Click it again to go back to light.
Close the preview with the X.
The width dropdown is worth using while you are in there. Checking the design at a narrow width and in dark at the same time catches most of what goes wrong on a phone at night.
What colour inversion does
Dark mode can invert colours unpredictably. Light or white backgrounds may become dark or black, and text and background colours can flip to their opposites. The result varies by client, which is why it is difficult to guarantee an identical result for every recipient.
In the preview you will see the pattern clearly: backgrounds go black, text turns light, and buttons darken, while your images do not change at all. That last part is the one that catches people. A photograph looks the same either way, but a logo saved on a white background keeps its white box and now sits in a bright rectangle on a black page.
Designing so it works either way
There is no setting in Bookboost that forces dark mode on or off for your guests. These are the practical steps that help.
Use logos and images with transparent backgrounds, so they do not sit in a white box on a dark background.
Avoid pure white and pure black as background colours, since those are the ones most aggressively inverted.
Keep enough contrast between text and background that the message stays readable if the two swap.
Add a visible border or outline around logos that would otherwise disappear against a dark background.
Test on a real device with dark mode on, not only in the builder preview.
What this does not do
You cannot control whether a guest sees your email in dark mode. That is their device setting.
The Bookboost preview toggle approximates the effect. It is not a guarantee of how any particular client will render the message.
Different email clients invert differently, so an email that looks right in one dark-mode client may still shift in another.
The toggle changes the preview only. Nothing about the campaign, and nothing a guest receives, is affected by leaving it on.
What to do next
For the rest of the editor, including the other controls on that same toolbar, see The email editor: a tour. To send yourself a real message and check it on your own phone, see Test your campaigns.
Getting help
Open Talk to Us in the left menu of the platform, or email support@bookboost.io. Tell us the campaign name, the device, and the email app where you saw the problem.