A student went out of the lab to talk on the phone and returned to find that their partner had neglected to monitor the ice bath used to chill their diazonium ion solution. To their horror, the diazonium ion solution was now sitting in a room temperature water bath. The student felt relieved that the diazonium ion solution did produce the brown aryl iodide product and para red dye.

But the students also noticed that the diazonium ion solution contained a fluffy yellow solid that later contaminated their final solid dye and altered its visible spectrum so that it had an unexpected maximum in the violet range of the spectrum. What was the likely identity of this contaminant? How did it form?