Without a photo, there is no way we could comment on the plant or what it might or might not need.

I too am not quite sure what this may be unless you have some honeydew left by insects like aphids, etc. When looking for insects, check several times during the day and at night. Look under the leaves, and in all branches.

Until you can post a picture again, I would just leave one more comment... japonica leaves suffer when they get afternoon sun during the summer months as it is too strong. But being in NC, maybe this is helping as the sun is a tad weaker. Sasanqua leaves can take all day sun but japonicas need afternoon shade and evening shade.

Thinking ahead... please comment where this mysterious iridescent change occurs: only on new foliage? only on old leaves? on ALL leaves? on a specific side/top/bottom? or only in random leaf locations?

The photos show more than I can actually see without magnification, which I don't have. A couple of the leaves seem to have curled up overnight, and that brown, dryish patch on the underside of the leaf is something that I missed yesterday, unless that turned up in the last 24 hours or so.

Bugs or their calling cards are visible in your second picture. Find out what kind these are before applying any chemicals.

luis, the bush is only about 15" tall. The iridescence is on the top of all leaves. I do not see anything on the branches. It does get the most sun in the afternoon, but it is filtered by a large lantana in front of it. There now is a dusting of something brown or dark on the backs of the leaves, but that could be because we had a fast but hard rain yesterday afternoon and some soil stuck to the leaves. The soil, by the way, is clay amended with Bumper Crop. The sasanqua does very well in it. It also receives bright light but very little sun as it is centered in an inside corner. Les is in the same area about 5-6 feet away, so not quite in the corner but against the house.

Ok, but keep an eye on the leaves during mid to late summer once Les outgrows the Lantana.

I also see some white spots in the second picture. Use a magnifying glass or take the picture and the same leaf -in a sealed, transparent plastic bag- to a local nursery for identification.

Will do, and thank you all for advice. Nurseries are few and far around here, but if and when I get to one I'll take a leaf in a bag and hopefully report something back to y'all.

You can get a magnifier at a drug store. You aren't really going to be able to rise to the occasion without one.

Agree.