There is no "global" way to change fonts or colors in a table. The formats of the individual elements, e.g., Title, Spanner, Caption, etc., must be individually modified to replace the 'default' fonts and colors. To do so, right-click on the element and choose Format (<name of table part>) from the menu to bring up the Format (Table Part) dialog.
There is also the option to change the default formats for each of these elements. The modifications will take effect immediately in ALL the tables. See Preferences and Default Formats for more information.
In both circumstances, specific or default formats, the font and color are changed in the 'Font and Color' section of the format (Table Element) dialog.

To change the font, click on the 'Change' button and select the font characteristics from the available list.
To change the text or fill (background) click in the color box and select from the choices given.
See Also: Preferences and Default Formats