White text on Black background?

I have an existing PDF created from writing software...

I want to change the title page so it has a black background [which actually is an image in faint grey lines on a black background]

and, have white text on top of the image bg.

this will give me the final document look I am after.

I can bring in my image, scale and position it as I want, but then when I put it to the background, it vanishes-

seemingly, behind a white background the black text is already placed onto?

but there also does not appear to be any way to change the text to white, nor can I remove the full-page-filling white background that 'seems to be there but cannot be selected'

is it not possible to change the background entirely?

I went to edit and create background from an image but when I applied I, it wasn't even there.

so I added an image instead and positioned and scaled it as described above- but again, same result once it is made the background.

[or just 'sent back'.

would really like to know if what I am after is even possible, because it would be a bother to create this separately in another program but if I have to I can stop wasting time with acrobat. the problem with doing this externally is getting the -exact-same- test scale and positioning that already exists.

thank you,

Au