Why has the ball changed for World Cup semi-finals?

[BBC]Fifa has introduced a new ball for the last four games of the World Cup.The gold and black Trionda Final ball will be used during the two semi-finals - France v Spain and England v Argentina, the third-place play off and Sunday's World final.On 6 July, Adidas and Fifa announced it would replace the Trionda Official Match ball, which adopted the colours of the host countries of red, blue, green and white and was used for the first 100 games of the tournament.The name 'Trionda' can be transla