I want to change the colouring (text and background) for when i am using blockquote “>” in my markdown in one of the pages. I am using the juice template.
The styling of elements such as blockquotes, backgrounds, text, will all be handled by the css of the theme. Some themes makes it easier to override styles than others. Your question would be best suited for the Juice theme github repo.
I did inspect element in firefox and it appears the styling is handled by .content blockquote {} so you would override that style, or find the relevant lines in the themes scss files and edit them directly.