You need to expose with more blue light to get more contrast with modern VC papers. The magenta filters pass both blue and red light. The paper is not sensitive to the red, but your eyes are, so the magenta filter makes the image easier to see. In a like manner, you need to expose with less blue light to reduce contrast. The yellow filters block some of the blue light and passes red and green. The green sensitive emulsion in the paper receives proportionally more exposure. The yellow filter allows you to see the image better.

For maximum contrast you can use a sharp cutting blue filter like Wrattan #47. You will have a very hard time seeing the image through this filter, but it usually gives a bit more contrast than the Multigrade #5. Blue filters designed for color work, like the 80B or the 82 series, pass all wavelengths. While they do increase contrast with VC papers, they are mot as effective as the Multigrade or Polycontrast filters.