2019-07-12 : Diamond Knight’s ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered.

2019-07-12 : If you somehow control a Diamond Knight for which no color was chosen, its last ability will never trigger.

2019-07-12 : You must choose one of the five colors of Magic as Diamond Knight asks you to choose a color. You can’t choose “artifact,” “colorless,” or “chartreuse.”