you can pinpoint a color in vray to be near the exact color by using a mathematical equation. it works well, but keep in mind that this may effect other colors in your scene. it is also vital that you are working in linear float for this to work. i often use this method to mathematically calculate my white point and ISO setting for perfect exposures.
http://www.cgarchitect.com/vb/170341-post2.html
.