Total Commander

As far as I know there is no way to define a background color for thumbnails. When there is a transparent image displayed in a thumbnail the background color of the file list is displayed.
Now when there is an almost white picture with a lot of transparency the whole thumbnail is white.

My current workaround is change the background color for file lists whenever I have to deal with such images. And then switch back to the normal color later.

My suggestion: Having a two color-grid as background for transparent thumbnails is the commonly known way to avoid the above described effect. It's used in most image editing tools.

Here is an example:
http://ghisler.ch/wiki/images/f/f2/Transparent_thumb_grid.png

Link to suggestion in Wiki:
http://ghisler.ch/wiki/index.php/Define_background_color_in_thumbnail_view

I think it would be more useful to specify separate thumbs background: specific solid color or standard two-color grid.

2MVV
What is the difference two my suggestion (except that a single solid color would never work?

Special color may also be useful, not only grid, so it may be customizable. Some images look better on solid colors. Anyway it should be better than using file panel colors (esp. in case of dark panel background).

A good idea in general, but wouldn't this be horribly slow, Windows-GDI programming-wise?
AFAIK TC now simply blends to the file list color.
When having a separate color, you need to paint a separate background for each Thumbnail.
I did some experiments like this some time ago, and it was a painfully slow, especially since Vista+ has questionable GDI performance.

In any case, isn't this something that plug-ins can do, when used for thumbnail/preview?
If I use Imagine to render Thumbnails for pictures files with an alpha part, it already pre-blends to such "checkered" background.

2MVV

Special color may also be useful, not only grid, so it may be customizable. Some images look better on solid colors. Anyway it should be better than using file panel colors (esp. in case of dark panel background).

There can be red, white, black, blue, green single color images with transparency. What color would you choose?

2milo1012

A good idea in general, but wouldn't this be horribly slow, Windows-GDI programming-wise?

No I don't think so. Having an alpha-channel these days is state of the art. In the end an alpha-channel has to be drawn only for images which actually have an alpha-channel (that excludes all holiday pictures). Once drawn it can be stored as such in the temporary and persistent cache. This way it becomes an ordinary image.
On the other hand changing the chessboard colors would mean all these thumbnails would have to be recreated. So I guess the actual drawing performance should be taken into account.

n any case, isn't this something that plug-ins can do, when used for thumbnail/preview?

Sure. I guess a better phrasing for the suggestion would have been 'add chessboard background when a thumbnail provider (Lister, Explorer, external program) returns a transparent image)'.