Luca, thanks for the reply to the problem of chessx not showing MultiPV lines correctly with Stockfish.
Specifically, I am using the Stockfish that comes with ChessX, "Stockfish-3-64".
As an example, try the position:
1q3R2/8/8/8/8/K1kBP3/3pP3/8 w - - 0 1
Set the "Lines" field to "2" in the Analysis window.
Mine shows two lines. The first has an evaluation of 84.23 and is in blue - White wins with R:b8.
The second line shows "Mate in 4" with 1. Rc8# , and is also in blue. But in that line, it's White who is getting mated, not black. And in fact the line shown ends with 4...Qa7#.
So why is the second line in blue and not in red?