"You must be brave," he said, and his voice changed subtly.
This was difficult, for Scarlett had not a subtle bone in her body; and Gerald was so much like her he never failed to penetrate her weak subterfuges, even as she penetrated his.
Do try to be more subtle, more seductive.
The questions were none too subtle but Pitty, in her pleasure at having a member of the family to talk to, did not even notice the bald way the questions were put.
He neatly deflated the pompous and exposed the ignorant and the bigoted, and he did it in such subtle ways, drawing his victims out by his seemingly courteous interest, that they never were quite certain what had happened until they stood exposed as windy, high flown and slightly ridiculous.
Something of her dilemma showed in her eyes for Johnnie’s expression changed subtly and some of the hardness went out of his face.
He went about his campaign slowly, subtly, not arousing the suspicions of Atlanta by the spectacle of a leopard trying to change his spots overnight.
not obvious, but understandable by someone with adequate sensitivity and relevant knowledge (perhaps depending upon fine distinctions)
capable of understanding things that require sensitivity and relevant knowledge (perhaps understanding fine distinctions)