Pages - Colour background insert new page!

Hi

I thought I would try to use Pages after so many years of using other things

I'm creating a page where I need to change the background to a colour. My understanding is I create a text box to the full size of the page and change the colour. I've tried this with a text box and a shape but as soon as I make the text box or shape to fit the page, Pages inserts another blank page. the only way I can remove the blank page is if i move the original text box or shape up the 1st page. So now I have a colour block on the original page and I want the original page to be full colour all over

What am i doing wrong? Is there an easier way to change the background colour of a page?