Could it be
zwischenzug (Chess & Draughts) chess a tactical move interpolated into an exchange or series of exchanges to improve the outcome [German: in-between move]
based on Rubios answer and your hint about the 'look in between' (also dazwischen) line?
You thought you could attack me.
But hold on, not so fast.
Look in between,
in between means "dazwischen" in German (=zwischen)
since German trains are best.
train means "Zug" in German (=zug)
No matter black or white,
hints at the solution having to do with chess.
if you did not consider,
my move is meant to look like it is totally obsolete while significantly changing the outcome.
You might've been winning,
But now I am the winner.
since you didn't consider my move to be important in any way you now have lost.
Big thanks to @Rubio your guess helped a lot.