In the middle game having opposite colored bishops means KING HUNT usually they end in mate and rarely ever (at a decent level) go to the endgame. Now in an endgame the opposite is true, opposite colored bishops are very drawish and very difficult to win, at a decent level an overwhelming majority of games end in a draw if there are opposite colored bishops in an endgame. So it would depend really if you are winning in a middlegame you want to have opposite colored bishops if you are losing then you would prefer same colored bishops. In the endgame all the contrary, if you are winning you would love to have same colored bishops but if you are losing an endgame you will wish you had opposite colored bishops.
Which color bishops question
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I agree with zxb995511
I'll throw in that your bishop preference also has to do with the pawns. In the majority of middle and endgame positions it's favorable to have your bishop opposite your pawn color, not only for mobility but also because they compliment each other (pawns guard one color, the bishop the other). Likewise it can be useful to force your opponent to move his pawns onto the same color as his bishop.
When center pawns are locked on the same color as a friendly bishop, the bishop is called a "bad bishop" although if you're able to get it outside of the pawn chain, or otherwise preform a useful function, it's active and valuable (although still technically labeled "bad"). In an endgame with your "good" bishop vs their "bad" it can be a winning advantage.
In fact in endgames you almost never want a "bad" bishop (and so would work to move pawns off of that color or as the opponent work to keep them on that color). Even so, often beginners will try to place all the pawns on the same color thinking they have made some kind of fortress, although in reality they have made their defensive task much harder.
I know this has been probably asked and answered, but I just can't find it with search on the forum. Which is better, if you and your opponent have one bishop, have them on opposite colors, the same color, or it doesn't matter?