I saw your video of how to remove a background in Preview. I do use the Smart Lasso, but I find that in order to get the right color background, I have to cut and paste the image onto that color and then take a screenshot of the whole thing. I note that in your video, the background that you remove is automatically grey. How do I change that color to the color I want?
I want my cut-out from Smart Lasso on a certain color background, and I want to know how to get that color when I delete the background sections I don’t want.
The background isn't actually gray. It is transparent. But the app have to show something -- it can't actually become transparent where you would see through your screen. So it has to become some color that visually indicates where it is transparent. You can actually change that color in Preview, Preferences, General.
So is your goal to put the subject on a solid color background? If so, changing this transparent color won't make a difference. If you export, it would be white, I think.
So one way would be to cut out the background, then select all, which would just be the subject, and Copy. Then use the Rectangle tool to draw a solid color over the whole image. Then Paste the subject back on top of that.