marker page number not going on second parent page

I'm a bit confused as to the query - but my understanding of the query maybe it helps.

Parent Pages are in Pairs

Side by Side in Parent Page layout they'll show A and A 

If you want B

Then you have to apply Parent Page B to the page in the layout. 

So if you're alternating page numbering colours throughout - then you need to apply Parent Page B to all pages that require it. Pretty sure you can multi select pages then Apply Parent Pages. 

However, this is a very complex way - if it's every odd page numbering is a different colour. You only need 1 parent page - and in the Parent Pages set the text colour for the right hand side page to be Red text. 

Now you only need 1 parent page. 

If it's spread out across odd and even pages - then you'll need 2 parent pages and manually apply the correct Parent Page to the layout. 

As pages add and delete etc you'll need to reapply the parent pages. So maybe do this at the end/final layout.

Hendy, it might be that both Parent pages are Prefix-named the same A prefix.

If you Opt/Alt click the label of the 2nd Parent page, it will show the Parent Options dialog box. 

Is the Prefix name B?

What is the Based On set to? None means a 2nd independent Parent page, while Based on "A" means a descendent child page of the parent page.

The parent page A will show a letter A, assuming you put in a Type > Insert Special Character > Marker > Current Page Number (Cmd/Ctrl+Opt/Alt+Shift+N). 

If you have Facing Pages checked on in Document Setup, then both the left and right A-Parent page will show an A.

Then later, after double-clicking to a physical page in the Pages panel, you should see that A marker show a page number.

@hendy_5450

Why one is red and another one is black?

They are,

I don't remember doing anything different whenever doing page numbers in a book

Do I have to change something?

Probably both are pages of the master/parant A,