Pilot Iroshizuku Syo-ro vs Ku-jaku

My Canon CanoScan LiDE 300 scanner does not seem to capture subtleties in green very well, and so leaves post-scanning colour-correction with not a lot to work with.

It didn't help that the two ink colours are nigh indistinguishable when written very wet, and somehow the Pilot MR's steel F nib appeared to be writing increasingly wetter with time, even though I didn't see any tine misalignment under a loupe, and the tine gap while seemingly wide for a Japanese nib did not appear to be the problem. Trying to close the tine gap didn't help; and neither did swirling the nib around briefly in dilute solution of aqueous ammonia and dishwashing detergent. I ended up smearing detergent directly onto the nib and rubbing it vigorously, then dunking it into >90°C hot water. That seemed to have more of an effect in taming the wild ink flow witnessed earlier.