http://www.ilford.com/html/us_english/pdf/Cont.pdf

If you go to page 3 of this PDF (and since it's a PDF and I couldn't just copy and paste) you'll see a section titled "Dual Colour Filter Settings." I'm not touting this as true (and I note now that it says "...but should need LESS adjustment to exposure times when changing contrast." not "no") just passing the information along I had read.