Default Body Font Size & Color

Hi There, 

1) Is there a way to reset the default paragraph font size? The 17 pt is so small compared to headings and subheadings. It looks unreadable on phones in particular. 

-If it can be reset, does it affect any of the responsive displays for other devices?

-If I manually reset the font size for each paragraph, will it cause issues with responsive displays for other devices?

2) Is there a way to set the default paragraph color to black? The dark gray is a little too low contrast for some learners using older displays. I've been manually resetting paragraphs to black.

Thanks!