Hi there. I agree with all the comments below, and would love to add my 2 cents :

UI designer's feature needed here.

If I'm building icons, by default Ai displays a white background. And when I want to work on white icons, it's of course not optimal.

The trick is to show the transparency grid, which by default is set to white and light gray.

I had a lot of white icons coming from CC libs (first coming from Ai files). And those icons would mostly be white and transparent strokes and fills (mostly white fills).

If Ai became smart enough to realize that a mostly white content document requires to be displayed on a dark background, then it saves me so much time.

Of course, make this a preference so users don't hate you for a dark transparency grid.

Cycling through transp grid color would be nice also.

And alt-click on the transparency grid button sending you to the document settings would have avoided me digging through the 20+ preference panels :)

I frequently create large amounts of web ads in Illustrator and need to create a background colour on each. It would be REALLY helpful if a background colour could be added at setup. I need the colour to export, so the workaround of 'simulate coloured paper' does not work.

SVG? SVG is a vector format. If there is nothing in the background, it will be transparent. You have to create a 'big box' underneath, that is how a format works.
To avoid it from being selected when you marquee your stuff —just move it to a separate layer and lock the layer, or just the background itself (but in this case you can accidentally unlock it Unlock All command when working on the design)

I agree. Depending on the colors we use for our art, it can get lost unless we hack it and create a new shape layer at the bottom of our stack. Not very intuitive. Should be and option to change the artboard and canvas color.

I always work outside of the “pure white” artboards, onto the darker canvas.

I do "export as" and choose SVG. I don't see such an option. I chose TIF, BMP, PNG and I don't see the option you are telling me about.

What format do you export your document to? What method do you use? Export As? Export for Screens? Save for Web?
Most of them allow to choose if you want transparent or opaque background.
If not (like TIFF and Export As, which is a miss), then you can can create your big rectangle and place it on a locked layer under your art — this will prevent it from getting selected.

Can I have a real non-transparent artboard? For example, if I am creating art to be exported into another document, I see my background being transparent which is not what I want.

I know I can draw a big box and put it in the back and make that big box non-transparent by filling it with some color. The problem with this is highlighting multiple objects with the mouse is hard because when you are trying to draw the selection box you select the big white box too which is not what you want.

So, can we have a real non-transparent background?

Being able to select a background colour other than white would be great for jpg asset export too.

Hugely agreed. Making a dark box as a background for every document is highly tedious. Changing to transparency grid and making both checker-box colors dark SHOULD work - but it doesn't because it messes with all your thumbnails and also makes a 'broken line' outline to your artboard. Please add this essential option asap.

It would be great it were possible to set a 'working' background colour for artboards e.g. upon export of the image / artboard it would default back to transparent or white (depending on output format).

Having worked through creating a number of white icons, you can get around it by manually drawing in background and turning the visibility off, but if there was an option on the artboards palette to do this, it would be much easier.

Agreed.

Agreed! I understand that for print documents "paper" color can change how printed media looks, but in 2019, the majority of users are probably creating work for screens almost exclusively. White graphics are almost impossible to create or edit in illustrator without using silly hacks or work-arounds.

It's a cruel joke that this function is still missing from Illustrator.

as Pierre-Francesco Costa said. But it would be nice if we could set the *default* grid colours to our choosing - e.g. dark for all (new) documents

Choosing a specific exported PNG background color could be really helpful for some of the UI designer. Specially for the ones who work with non transparency supporting environments.

Right now if I choose a dark interface for Illustrator, my two choices of canvas color are dark gray or pure white. Why can't I pick an abritrary shade of gray?

View > Show Transparency Grid

then

File > Document Setup

You're welcome ;)

this is needed asap please... doing all white text designs is impossible with the default of white in edit mode. the workaround is to place a colored rectangle, then remove it on export.

More importantly, exporting artboards with a rectangle as a"background color" is highly error-prone. I have on multiple occassions exported a file, only to have someone else catch a 1 or 2px white border. I have to tediously adjust the rectangle and re-export. Artboard background colors would make this mistake impossible.

Object > Artboards > Fit to selected art