Whilst not helping with colours that have already been mixed, but going forward, I would add that in AR Vitae the user dose have some ability to tweak and customise the colour blending engine used in ARV.
It can be accessed by going to: Tools > Colour Options > Paint Mix Profile Panel.
From that panel you can also access the Paint Mix Presets panel which contains a couple of other options other than the Default blending.
And of course you can always Save your own custom colour blending presets too.