In my Blender project, there are 2 two-dimensional mesh objects. They both have the color white. In the "solid" view they indeed show up white. However, when rendering a video or picture ("rendered" view), they take the color of the "world" (which is blue). So they only become visible (in blue) when there are other objects in the background.

How can I make these object show their intended color (white) in "rendered" view (and therefore in any baked picture or video)?

PS: I have tried giving the objects other colors than white, and then there is no problem. So only when they are white they take the color "world" whatever that color is.