When making a new image with the following settings in "Content"



Background set to "As First Layer" in the "Content" tab.

Doing this awards your document with a "Layer 1" that is filled with the color you've chosen. If you want a fully transparent image, you have the option to do so here by setting the Image Background Opacity to 0% if you wish. Otherwise, the layer will be filled with the color.

As you are likely aware, this is no ordinary layer. It is different from if you were to make a new layer and fill it with a paintbucket. The color you selected when you made the new document is now infinite and stretches on forever. Additionally, if you were to draw something on it in black and then hit the Delete key, instead of setting all of the pixels to transparent, it sets them all to that background color, but only if no selection is made. A lot of tools fill all transparent pixels with white, actually, but only when nothing is selected.

In this situation, if I press CTRL+T and drag...
It leaves behind transparent pixels.

However, if you don't have a selection... It replaces transparency with your background color.

This is quirky but not really a problem except for one strange issue... There's no way to visually distinguish a layer that has a Background Color attached to it, that I can find.

Nothing in layer properties:

Changing image -> "background color and transparency" to a different color doesn't seem to affect this layer.

I'm wondering if there's something I'm missing? Like if there's an option somewhere that I'm not seeing that reveals the mystery of these layers.

This because the background layer is a layer with a 'default' pixel set to white. All other layers ave such a pixel, but they're set to transparent. We've never had the time to implement a toggle to configure this.

@remeranAuthor

In krita (as in GIMP), I never use the background layer for painting on; I always use transparent layers above the background. I do this because the background layer has different behaviour from other layers and can be confusing. In krita, there is different behaviour between different tools such as Move and Transform (position) and also whether areas are selected or not, as you've noted in your post.

I can understand why the background layer is provided but I find it's best to only use it as a coloured (or white) background and nothing else.

Note: All layers are 'infinite' in that you can paint on them and move that 'off canvas' where it will be preserved. This is very useful, especially for animation where background scenes and characters can be made to 'slide' into and out of view.