Hi Matadem, for the background color you can go to Options > View > Colors > Background color.

You can change that to "Custom" and click on the color swatch that will appear next to it.

With that method the background color there will be used overriding the current theme.

You could also leave that to "From theme" and instead make a new theme under Options > General > "Manage themes". If you do it this way you can switch between themes.

The line color comes from the Style that the object is assigned to. Go to Scene Browser > "Styles" and Ctrl+click on black color swatch for the Default style and set it to white. To make these styles used for startup save a .3dm file and set it as the template file under Options > General > "Template file".

There is also another way you can force all dimensions to use a specific color instead of it coming from the style assignment. That's in moi.ini under

[View]
AnnotationColorMode=FixedColor
AnnotationFixedColor=255,255,255

That's for dims and text, for curve objects like lines it's this:

CurveColorMode=FixedColor
CurveFixedColor=255,255,255

- Michael