Solar Orbiter (SolO) is a planned Sun-observing satellite, under development by the European Space Agency (ESA). Due to its proximity to the Sun, it receives about 13 times more solar energy than we receive on Earth, causing the temperature of its sunward-facing side to soar to 600°C. So there must be a Thermal Protection System (Heat Shield) to prevent the spacecraft from melting. ESA's webpage gives the following explanation:
To protect the spacecraft and payload, a high-tech heat shield has been designed that is made of several protective layers of titanium, the outer of which is coated with a protective skin called “Solar Black", which has been developed specifically for Solar Orbiter.
We know that any spacecraft gets heated by the Sun due to Thermal Radiation. White colour is a good reflector and a poor absorber of thermal radiation. On the other hand, black colour is a good absorber and a good emitter of thermal radiation. According to me, white is the best choice of heat shiels, as it is far better to reflect the radiation instead of absorbing it and emitting it. If you remember properly, the Parker Solar Probe, also had a heat shield, but its sunward-facing side was white in colour, and not black.
The following rendering shows that the heat shield is black in colour:
The following image shows only the heat shield ready to be tested in a Thermal Vacuum Chamber:
Image Source: Solar Orbiter sunshield
I don't understand why is the sunward-facing side of ESA's Solar Orbiter is black in colour, instead of white. Why did they choose black over white (on a thermodynamic basis)?
A few differences, which I could think of between Parker Solar Probe (PSP) and Solar Orbiter (SoIO), relevant to our analysis are as follows:
Distance from the centre of the Sun: PSP - 9.86 solar radii (6.9 million kilometres or 4.3 million miles); SoIO - ~60 solar radii
Material of the Heat Shield: Question/Answer regarding PSP