Sometimes black strokes are fine, and then they become a lighter color - kind of a faint bluish color. I'm a newbie, and I tried all I could see in color for strokes and fill to make things a true black to no avail. Opacity is set to 100%

Am I changing something inadvertently to make the change in color? Is it possible there is something in the program that makes it switch?

What can I do to remedy this?

Never experienced such here.
Do you see the blue-ish black at the fill and stroke panel as something like (0,0,23) in the rgb field?
If there the black appears as (0,0,0) your screen displays a different colour.
Maybe you see the difference because dynamic contrast and back-lighting?