The air shroud in Supermicro systems, including those with Direct Liquid Cooling (DLC) solutions like the SYS-421GE-TNHR2-LCC, is typically designed to direct airflow (or in hybrid systems, assist with liquid cooling efficiency) and is made of plastic or composite materials. Based on Supermicro's standard design practices seen in technical documentation and product images (e.g., SYS-420GP-TNAR, a similar GPU server with DLC), the PCIe tray's air shroud is consistently black. This color aids in heat absorption and dissipation, aligning with Supermicro's focus on thermal efficiency in DLC systems, where cold plates and coolant distribution units (CDUs) manage heat directly at the chip level. White or clear shrouds are less common due to aesthetic and thermal considerations, and "opaque" is not a specific color designation. Thus, black is the correct choice, reflecting Supermicro's engineering standards for high-performance computing components.
References:Supermicro product images and manuals (e.g., SYS-420GP-TNAR User Manual), general DLC solution descriptions.