The second screen of the menu Option\Preferences is used to set the colors being used in MesNews:

Zone Marked messages :

Messages can be marked so it is easier to find them back. You can do this by setting a rule in rules of messages, or by marking a message in the menu Messages\Mark\Mark message, Or by right clicking on the message. This zone lets you set the style and color of the marked messages:

Style of message : tick the boxes Bold, Italic and/or Underlined to change the style of the message in the tree.
Use the default color : when ticked the message will show a different style (bold, italic,or underlined) but will not get a different color (it will stay black or in the color that it is given by a filter)
Fix the colour of the marked message : If the previous box was not ticked the the marked message will get the color set in this zone.

Zone Mark message :

When you mark a message in a discussion it is not so easy to find it back when all treads are closed. By ticking the box When selecting message also select source, the message of the source of the tread is also marked. When you remove the marking from the message then the marking of the original message is also removed.