Ventoy Theme Looks Right in Plugson but Not at Boot Diagnosis

Plugson's preview says your theme is applied; the boot menu disagrees. The preview reads files - the boot menu reads parsed settings. Here is how to find where the two stopped matching.

By Technical AnshuVentoy Theme Guide7 minute read

Watch the video for the Plugson and boot-menu screens compared side by side

This is the most confusing Ventoy theme problem: inside VentoyPlugson everything looks perfect - your theme is selected, the preview shows your wallpaper - yet the actual boot menu still opens with the default theme. The reason is simple once you see it: Plugson shows you files on a disk; the boot menu obeys ventoy.json as Ventoy parses it at boot time. Those two can disagree. This guide finds out where they parted ways.

F5 Tools at boot - Check plugin json configuration

F5 Tools +-- Check plugin json configuration | +-- Check global control plugin configuration | +-- Check theme plugin configuration <-- your theme, as parsed | +-- Check menu alias plugin configuration | +-- Check menu class plugin configuration

At boot, this menu shows the configuration Ventoy really loaded - the ground truth when Plugson's view and the boot menu disagree

Did the Settings Actually Get Saved?

Plugson is a small local web page that edits ventoy.json - but an edit only counts once it is written to the file on the drive. If you changed the theme, admired the preview and closed the Plugson window or browser tab without applying/saving, the file still points at the old theme. Reopen Plugson, make the theme selection again, save it, and only then close Plugson from its own window before unplugging the drive. Then open ventoy/ventoy.json in a text editor and confirm with your own eyes that the theme file line names your theme.

Are You Editing the Drive You Are Booting?

With two USB drives connected, Plugson may be editing the other one - check the drive letter in Plugson against the stick you actually boot
A copied ventoy.json on your PC's desktop is not the live file; the live one is ventoy/ventoy.json at the root of the stick's data partition
If you keep both a work-in-progress theme on the PC and an old one on the stick, the boot menu faithfully uses the stick's old one
Rule: after any Plugson session, open the file from the USB drive itself and read the theme path line

Ask the Boot Menu What It Parsed

Stop guessing and ask Ventoy directly. Boot the stick, press F5, and open Tools - Check plugin json configuration - Check theme plugin configuration. Three outcomes tell you everything:

Your theme is listed with the right path - the config is fine; the problem is inside the theme folder (a missing image name in theme.txt) or the resolution
An old theme or no theme is listed - Ventoy is reading a different ventoy.json than the one you edited; go back to fix 2
A JSON error is reported - one syntax mistake makes Ventoy skip the settings; the menu falls back to defaults while Plugson still showed your selection

Check Mode and Resolution Fallbacks

Two quieter causes remain. Ventoy supports different themes per BIOS mode (Legacy and UEFI) through its multi-mode settings - if a theme was set for one mode only, a machine booting in the other mode shows the default. And if the gfxmode in your theme block names a resolution the test machine cannot do, GRUB can fall back to a plain menu that looks like the theme never loaded. Test with "gfxmode": "max" to rule this out, and always do the final test as a real boot - a Plugson preview can never show you a firmware fallback.

The habit that ends this class of problem forever: one change, one real boot. Change the theme in Plugson, save, boot the stick and look. Ten small verified steps beat one big editing session you have to debug blind.

Watch the Full Setup in the Video

The video shows both views of the same theme - useful while you compare yours.

Watch Full Video

Frequently Asked Questions

Does VentoyPlugson apply changes immediately?

Plugson writes your changes into ventoy.json on the drive when you save them in the panel. The boot menu only ever reads that file at boot time - so an unsaved change, or a change saved to a different drive, never reaches the menu. Always confirm the theme line inside the file after a Plugson session.

What does Check theme plugin configuration actually show?

It shows the theme settings Ventoy parsed from ventoy.json during that boot - the file path it will load, and any problem it found. It is the ground truth: if your theme is not shown there, the boot menu was never going to use it, whatever Plugson displayed.

Why does the theme work on my PC but not on a customer's older PC?

Most often the older machine boots in the other BIOS mode (Legacy instead of UEFI) or cannot use your gfxmode resolution, so GRUB falls back to a plain menu. Test your final stick in both modes and with gfxmode set to max before calling the theme finished.

This guide is based on the Ventoy Custom Wallpaper Setup video by Technical Anshu - Add Your Branding - Stuck on a step? Ask in the video comments, help is always there.