Windows Themes and Wallpaper: Why Yours Says Custom

You opened Personalization to change the wallpaper, and the theme at the top of the page now says Custom. Nothing has gone wrong.

A theme is a bundle of several settings at once, and touching any single one of them quietly moves you off the named theme. Almost every Windows PC ends up there.

I pulled the theme name off this PC before writing, and it was that exact word.

What a theme actually bundles

The part that explains everything else on this page.

⭐ A theme is four things saved together: the desktop background, the accent colour, the sounds, and the mouse pointers.

⚡ That is why the list at the top of Personalization looks like wallpaper and is not. Picking one changes your pointer scheme and your system sounds too.

⚠️ And it is why yours says Custom. Change the background on its own and the bundle no longer matches any saved one. Windows then stops naming it.

Microsoft's route for the background itself

The documented half, and it is the half most people want.

Documented by Microsoft on its desktop background page: "Select Start > Settings > Personalization > Background."

Microsoft names four choices for what to put there: Picture, Solid Color, Slideshow, and Windows spotlight.

⚠️ We could not find any discussion of themes on that page. It covers the background and stops there, which is a fair part of why the two get confused.

⭐ Windows spotlight is the one that changes daily by itself. If your wallpaper keeps changing without you, that setting is why.

Ours: what this machine reported

Four values, and the first one is the whole point.

Ours, and read on the PC used to write this. The current theme came back as Custom.theme. Apps and system were both set to light, and the wallpaper fit value was 2.

⭐ And Windows ships with seven themes of its own here. Fewer than the page suggests.

⚡ Put the same question to your machine. Nothing is changed:

Get-ItemProperty "HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes" |
  Select-Object CurrentTheme

⛔ Custom.theme is the normal answer. It means somebody changed one setting once, which is nearly everybody.

Light and dark are two settings, not one

The pair that catches people out constantly.

⭐ Windows keeps a separate mode for apps and for itself. On this machine both read light, but they can differ.

⚡ That is how you get a dark taskbar with white app windows, or the reverse, and think something is broken.

⚠️ Both live in Settings, Personalization, Colors, under "Choose your mode" with a Custom option that exposes the two separately.

⛔ Neither of them warms the screen colour at night. That is a different feature and it is already built in.

Fit, fill and the stretched wallpaper

The setting behind a picture that looks wrong.

⭐ The dropdown under the image is what decides it: Fill, Fit, Stretch, Tile, Center and Span.

⚠️ Stretch is the one that distorts. A picture that looks squashed or oddly wide is almost always set to Stretch. Fill is the fix.

⚡ Span is for more than one screen. It only helps if you have a second display attached.

⚠️ The stored value is a number, not a word. Microsoft's page does not publish what each number means. Trust the dropdown instead.

Saving your own, so it survives

Thirty seconds, and it is the answer to the Custom problem.

⭐ Set the background, colour and sounds you want, then press Save on the theme list. Give it a name and it stops being unnamed.

⚡ A saved theme survives a reset of your personalization. It can also move to another PC. A theme is a small file rather than a setting.

⚠️ The picture is copied, not linked. Deleting the original photo afterwards does not break the theme.

⭐ Ours, and marked as ours: save one before you experiment. Getting back to a look you liked is otherwise entirely from memory.

What a theme will not do

Being clear about the edges, because expectations run high.

⛔ It does not change your lock screen. That is set separately, and so is how quickly the machine locks itself.

⛔ It does not touch icon size, text size or scaling. Those are display settings. Different part of Settings entirely.

⚠️ And transparency is not part of the bundle either. It sits with the visual effects switches, which is a separate page again.

Status: written against Microsoft's desktop background page and checked on Windows 11, 25 August 2026. That page gives the Settings, Personalization, Background route and the four choices of Picture, Solid Color, Slideshow and Windows spotlight, and we could not find themes discussed on that page. The current theme name, the light and dark values, the wallpaper fit value and the count of seven shipped themes were read on this PC.

Why does my Windows theme say Custom?

Because a theme bundles the background, accent colour, sounds and pointers together. Change any one of them and the bundle no longer matches a named theme. Almost every PC ends up there. Nothing is wrong.

How do I change my desktop background in Windows 11?

Start, then Settings, then Personalization, then Background, which is Microsoft's own route. From there you choose Picture, Solid Color, Slideshow or Windows spotlight as the source for what appears.

Why does my wallpaper keep changing on its own?

Windows spotlight is selected as the background source. It supplies a new image regularly by design. Switch the source to Picture and choose your own file if you want it to stay put.

Why does my wallpaper look stretched or blurry?

The fit dropdown under the image is set to Stretch, which distorts a picture that does not match your screen shape. Fill crops instead of distorting. It almost always looks better. A blurry result usually means the image itself is smaller than the screen.

Can I move my theme to another computer?

Yes. Save it from the theme list first, which turns it into a small file including a copy of the picture. That file can be carried to another Windows PC and applied there.

The Short Version

• A theme bundles the background, accent colour, sounds and pointers together.
• Change any one of them and Windows stops naming it, which is why yours says Custom.
• This machine reported Custom.theme, and seven themes shipped with Windows.
• Settings, Personalization, Background holds Picture, Solid Color, Slideshow and Windows spotlight.
• Spotlight is why a wallpaper changes daily without you touching it.
• Light and dark are two separate settings, for apps and for Windows itself.
• Stretch is the fit option that distorts a picture. Fill crops instead.
• Save your own theme, and a look you liked stops depending on memory.

Where to Next

Open Settings, Personalization, Background and look at which of the four sources is selected. That single line explains most wallpaper complaints.

If the picture looks wrong, change the fit dropdown from Stretch to Fill. It crops slightly and stops distorting.

Then save your theme once you have it how you want it. A name costs nothing and it survives things that would otherwise wipe the look.

Should your theme keep reverting to something you did not choose, tell me which build you are on in the comments. That one is worth chasing properly.