You can set the site-wide text font and colour for your website. This becomes the default formatting for your text. Remember that the formatting applied in the Text Widget overrides the site-wide formatting.
Navigate to Site Settings > Text.
Here you can choose your desired font and colour. Note that you can add your own colours to the colour palette by adding a hex code in this area, as highlighted here:
Once you have selected your default font and colour, click Save.
The colour and font changes will now be implemented site-wide.