When I visit the website with the theme Montoya, on the preloader a white rectangle appears in the middle (I believe it is the "Loading" text) and another large rectangle zoom in to full screen in white as well.

I want to change the color from white to black so I can keep all the website consistent.

To clarify more about the issue please find the video attached with this ticket.  

Hello,

at first, Montoya is really a great themes. Unfortunatly your solution doesn't work. The preloader screen ppears white.

The hex color code should be #000000 not #fff for black!! ;-)

Hi, I tried as you suggested. It worked. But there is still a split of a sec of a white screen when the website is loading.

You can check it here: https://mohamadchalak.com/

Also, I find that it's hard to edit/add new sections for a specific page.

Your screen is grey. Are you sure to take the #000000 (6 times zero)?

Yes, the screen is grey (#1b1b1b). So the visitor would know that the website is loading instead on a pitch black screen...