It’s practically impossible to think of California painter Wayne Thiebaud as a controversial artist. His creamy, deliciously reductive paintings of cakes, ice cream cones, gumball machines and trays of delicatessen food are beyond the negative reach of most critics. Even his pictures of exaggeratedly Alpine San Francisco street intersections and semi-phantasmagorical views of the Sacramento River are more friendly than weird. But a wall text in “Wayne Thiebaud, Draftsman,” his current exhibition of 83 drawings...