color of object becomes transparent in adobe illustrator

[Azhar22558182z5r2]

in illustrator, I have set the colour of the artboard black and when I'm trying to set the colour of the object then it becomes transparent.

[Ton Frederiks]

You are trying to simulate black paper and this is what happens when you print on black paper.

If you want a black background, don't change the paper color but just make a black rectangle in the back.