Lot of replies saying that you get no colour change with MGIV when Jmal has said that he does get a change, to purple, and he doesn't like it. As it happens I Selenium toned some MGIV RC for the first time ever last week and I too saw a noticeable change to purple. I've been toning MGIV Fibre for a few years and agree that it shows only the most marginal of colour changes, from a green to a purple. But the RC changed a lot more. No side by side comparisons needed, clearly purple.
So my answer to Jmal would be to try the Fibre.