Yeah, human vision (and that of other mammals and other animals) doesn’t tell the whole story about the spectrum of light. But that’s not really relevant, here. Any given spectrum has some color that it will be perceived as, and that’s all that matters for this question.
Consider, say, copper sulfate. If we shine a light on some copper sulfate crystals, or a solution of copper sulfate, and look at it from the side, we’ll see a spectrum that we describe as blue. If, instead, we shine the light through the crystals or solution, and look at the light that’s coming through, we’ll still see light that we describe as blue. No matter how we look at copper sulfate, it always looks blue. So we might as well just say “Copper sulfate is blue”.
But now consider air. If we take a bunch of air, and shine a light at it from the side, and look at the air, we’ll see light that we describe as blue. But, if we shine the light through the air, and look at the light coming through, we’ll see light that we describe as red. Does this mean that air is red, or that it’s blue? Or both at once? I don’t think anyone would say that it’s purple. Air behaves very differently from copper sulfate, in this regard.