Hi,

These are the colours used in ctg books. Note that the colours only have any influence on engine play if Tournament Book is ticked in Book Options :

Black  - program will play the move based purely on statistical performance in tournaments ie. if the statistical performance is good it will be selected.

Green -  program will play the move regardless of the statistical performance.

Red   -  program will NOT play the move regardless of the statistical performance

Blue  -  dubious move

Grey - the move was never actually played in any of the games in the dtaabse the book was made from, but leads to a position that results from some other line

If you right click on a book move the top 2 entries you see allow you to mark the move with a punctuation.  The top set are to mark a move and the second set down are to mark a position.  A Blue move is a move that has been marked as ?! which means "Dubious Move".  The other ways you can mark a move and a position are are:

For Moves:

??: Blunder
  ?: Mistake
?!: Dubious move
!?: Interesting move
!: Good move
‼: Brilliant move

For Positions:

∞: Unclear
=/∞: With compensation
=: Even position
+/= (=/+): Slight advantage
+/− (−/+): Advantage
+− (−+): Decisive advantage

Hope this helps you,

Mark