I suppose you are using the ribbon mode because that is the default user interface mode. Select ribbon tab Layout. The second item Themes in first group Look and feel has a down arrow. Click on this arrow to open a pop-up menu to see the pre-installed themes. I suggest to select once one after the other to find out which one is best for you. The webpage themes contains more user-contributed themes which could be also tried by you.

Clicking on the item Themes or the first menu item Manage themes in the pop-up menu opens Manage Themes dialog. On tab Editor is the last but one item Spaces, tabs, line ends. Configure the colors for Spaces, tabs, line ends to whatever you like most. The chosen colors are immediately applied on text in active file below the dialog window on having the magnifying glass symbol activated at bottom left edge as by default without saving the modification. The modifications are saved on clicking on button Apply (save and keep dialog window open) or button OK (save and close dialog window).

The same options are available on using toolbar/menu mode with contemporary menus by clicking in menu Layout on submenu Themes.

The submenu Themes is in menu View on using toolbar/menu mode with traditional menus.

The user interface mode can be changed at any time by right clicking on ribbon, menu or toolbar and clicking in context menu on appropriate command to change the mode.