In which case that grey scale and those swatches are useless. Removing the paper yellowing reveals the colours more as they would have been originally, but without knowing the hue and intensity of the original inks, a faithful restoration isn't possible. Here's a quick edit that restores the base paper (mostly) to near-white. You can see that it makes a nonsense of any external 'reference' colour. So the choice is eye-and-emotion versus instrumentation. Your choice, but personally I'd go with the Mk1 eyeball.