Early spider mites or dry-air stress

What's happening

Before mites spin visible webs they're already feeding, leaving leaves looking faintly speckled, dull, and dusty as cells are drained one by one. At this early stage the colony is small but growing, and the warm, dry indoor air that croton sits in is exactly what lets it explode. Catching it now, before webbing appears, makes it far easier to beat.

How to fix it

Inspect the leaf undersides closely, ideally with a magnifier, looking for tiny moving specks. Wipe the leaves down with a damp cloth to remove dust and any early mites, then treat with insecticidal soap, coating the undersides thoroughly and repeating every several days for a few weeks. Boost the humidity with a pebble tray or a small humidifier nearby, since the dry air is half the problem — humid conditions discourage mites and keep croton's leaves from drying and stippling.

This is general guidance based on common symptoms; individual plants vary.