There are a few youtube videos on the same subject. It's seems to be something benign that occurs with more than just VRP. Mobil 1 turns red in SD's Honda. It seems to be a benign nothing burger.
if it were my formula I would probably take all additve at 1-2% in base oil and add you used oil to see exactly which one is causeing a color change i would bet on alkaline or acidic additives maybe phenolics also
You drop red liquid in a semi clear to honey colored liquid and it's going to turn red. This isn't any kind of test other than red spreads.
It's as valid as cherry kool-aid turns ginger ale red so there must be something strange going on. No, and diluting cold oil with old cold oil tells you nothing.
This is Mobil 1 0w40 doing some cleaning in an GM 3800 V6. The piston in the middle is partially obstructed by the pickup tube but you can see where the red coloring is coming from. After about 3 more OCI and it stopped coming out with a red hue and was just dark.