change text color for whole website?

Hi,

So I love the square theme, but the text is a dull gray color which is a problem for me since my background is a dark color. I was hoping to change the text for everything(sidebar, content, footer) to a white color but I cannot find where to change it at in the editor. Every color change I make seems to have no affect. I saw there was a way to change the text color of a post when posting it, but that doesn’t fully solve my problem as I need the entire website to have white text. Can you show me what to change in the editor? I have some coding background and should be able to change it once I know what exactly is needed changed. Thanks.