How do I know that my red is the same as everyone else's red?
You cannot truly know if your perception of red is the same as everyone else's. The experience of color is subjective and can vary from person to person. We all have unique biology and individual visual perception, so it's possible that the way you perceive red might differ slightly from others.
While we can agree upon certain standards for defining colors and use color charts or Pantone systems to communicate color accurately, the actual experience of seeing and perceiving color varies. Two people might both call a color "red," but they may perceive it differently. However, since language and social conventions have established that a particular wavelength of light is perceived as "red," we refer to it as such.
It's important to understand that color perception is influenced by factors such as genetics, environment, cultural upbringing, and context. So, although your subjective experience of red may not be exactly the same as others, we can still use language to communicate and understand color in a relatively consistent manner.