The easiest way to go about changing the colors, however, is to set a different theme.
This process doesn’t clear other settings, it just essentially disables all custom settings except for global override for each particular categorized checkbox. Each one will completely override all other styles set in the configuration or theme only to display what the Global override is set to. In the Global override style, there is a total of 8 checkboxes. Note the background color is the canvas and the foreground color is the text color. And both the background and foreground colors can be changed. The font family and size can be adjusted as well. You can set for things to be bold, italic or underlined.
These are the Default Style and the Global override. If you want to immediately customize things, there are two main (separate) styles to look at. This option is found under Settings > Style Configurator. In Notepad++ the fonts and colors are controlled by the built-in Style Configurator.