Roseola

A 13-month-old previously healthy female infant presents with a 4-day history of high fever (40.2°C) without an obvious source. She had a brief febrile seizure but remained playful and interactive with good oral intake between fever spikes. Sepsis workup was normal. Today, her fever has abruptly resolved and a rash has appeared. On examination, she is now afebrile and non-toxic-appearing. The structure marked **A** in the diagram shows the characteristic rash. Which clinical finding best describes this rash and supports the diagnosis of roseola infantum?