I have a couple more 'top-and-bottom' pictures this morning, but first, here is a little composite of four Lime-speck Pugs, the slender little scrap whose resemblance to a bird dropping is thought to give it extra protection, birds not being given to eating their own poo.
This theory has flaws, I suspect, in that birds' vision is different from our own, and the Lime-speck's similarity to a dropping is very much a conclusion reached via human eyesight. I mentioned only yesterday how moths resting inertly on the trap top are clearly visible to us but go apparently unseen by the usually voracious and inquisitive robins, blackbirds and magpies which are well aware of the trap as a high class restaurant.
I put the pictures together to illustrate the slight variations common to almost all species of UK moths, just as we have countless little differences between us in the human race. The second Lime-speck is much less clearly patterned than the others, while the top one has a more jagged white line at the wing edge than the two at the bottom. In less distinctive species, this accounts for my hopelessness in giving accurate IDs. I am sorry that the photos are not better but I am still relying on my limited - albeit faithful - iPad Mini.
Here are the top-and-bottoms: another Willow Beauty which thoughtfully chose a clearer section of the cowl than yesterday's; and a Blood-vein. In both cases you can see that the patterning is essentially the top wings' showing through to below (only sketchily, too, in the case of the Willow Beauty), rather than a whole separate coat of scales in a different formation or colourway. The underneath of a moth is seldom seen at rest which would account for the drabness common to most species; but since it appears in flight, albeit only very fleetingly as moths jink violently about, it is perhaps surprising that none - to my knowledge - have more vivid colours to deter birds zooming from below.