Yes, all forms of electromagnetic radiation, including visible light, travel at the speed of light in a vacuum. According to our current understanding of physics, the speed of light in a vacuum is a fundamental constant denoted by "c" and is approximately 299,792,458 meters per second (or about 186,282 miles per second).
In a vacuum, such as outer space, electromagnetic waves propagate at this constant speed. This means that regardless of the wavelength or frequency of the electromagnetic radiation, all photons (particles of light) travel at the speed of light.
However, it's important to note that light can be affected and slowed down when it passes through certain materials or mediums other than a vacuum. This phenomenon is known as the speed of light being "slower" in a medium. When light interacts with matter, it can be absorbed and re-emitted by atoms and molecules, which leads to a delay in its propagation. This results in a reduced effective speed of light through that particular medium.
The speed of light in a medium is typically denoted by "v" and is less than the speed of light in a vacuum (c). The magnitude of this reduction depends on the optical properties of the medium, such as its refractive index. Different materials have different refractive indices, which determine how much the speed of light is slowed down as it passes through them.
So, while light can be slower than the speed of light in a vacuum when traveling through a medium, it always travels at the speed of light in a vacuum, which is a constant in our current understanding of physics.