As we know, colors only exist in the brain. How can we see light if it has no color? Our eyes detect light, but seeing occurs in the visual cortex. Is visible light really visible?
In this context, "visible" means "within the range of frequencies that elicit a response in the human vision system that results in the perception of light".
There are other meanings of the word "visible" that are different but related. Nitrogen gas is invisible, but chlorine gas is visible. You are visible, but Casper the Friendly Ghost is sometimes visible. In these contexts, by "visible" we mean "can be seen". Light, in itself, cannot be seen in that sense. So we cannot apply this definition to light.
This is somewhat like the various definitions of "heat". The different definitions of that word are applicable only in particular contexts. A particular meaning cannot be applied to a context to which it does not apply.