Coronal mass ejections consist of a very hot, but thin, plasma. Their very weak intrinsic emission would be dominated by ultraviolet and X-ray lines and bremsstrahlung continuum. There is very little optical radiation.
However, CMEs can and are monitored at optical wavelengths using the light that they scatter from the Sun. The process is Thomson scattering from the free electrons in the plasma. This is done by spacecraft because the Earth's atmosphere makes it very difficult to achieve the contrast necessary to observe the scattered light close to the Sun (except during total solar eclipses).
A CME takes a couple of days to travel from the Sun to the Earth and such monitoring can give "space weather forecasts" associated with magnetospheric phenomena triggered by the impact of CMEs.
An example picture taken by the LASCO white light imager on board the SOHO spacecraft is shown below. Everything here is viewed in scattered light. The Sun is obscured by an occulting disk.I have picked an example showing the eruption of a CME.