Nothing else really to do then after that (!) except head off to the opticians. First stop was at a well known high street chain to see if they could repair my dad's ancient specs (two broken arms) and put prescription lenses in? I think they thought I was off my trolley.
So, without much hope I went to the local independent opticians in the small market town where I live and while they thought the specs almost beyond repair, they said that they'd send them off and see what could be done – and now, brilliantly, and not expensively, the specs are as good as new and I can see to draw again! (my eyes aren't that bad, but even to lose a small amount of clarity I've been finding has meant drawing has become more difficult as well as tiring).
Snakes Head Fritillary (Fritillaria meleagris) have a honeycomb/check on their petals that has something of the bleed effect of tie-dyed fabric. Muted purple petals, a vivid flash of yellow from the stamen, alongside a rather splendid shade of stem green and I can see that quite clearly...
...from my seasonal colour sample notebook.