@Martha we can reproduce the black SVGs, we are going to fix that.
In the meanwhile, you can copy the CSS files below into your User-Data Folder (Help > Show User-Data Folder). This will make your drawings show on the default thumbnail background color (feel free to adjust the color in the CSS files to white, if you prefer that).
style-light.css (70 Bytes)
style-dark.css (71 Bytes)