Although it's not shown in the film, Jake divorced Ida, his first wife, in 1945 to marry Vikki Thailer, whom he met at a swimming pool and with whom he remained until 1957.
There are actually a few reasons. According to Martin Scorsese's the DVD commentary, when first screening some test 8mm footage of Robert De Niro sparring in a ring, he felt that something was off about the image. Michael Powell, who at that time had become something of a mentor and good friend to Scorsese, suggested that it was the color of the gloves that was throwing them off. Realizing this was true, Scorsese then decided the movie had to be filmed in black and white. In the commentary, they said they had to change the color to a dull brownish so they could get it approved with so much blood. They also mentioned that as being one of the reasons Raging Bull was not shot in color-too much blood even for an R rating. The film being in black and white also helped it to differentiate it from other boxing films that were being released around that time, such as Rocky II.
