Saussure in his theory of signs declared that there was no necessary connection between the semantic value of a word and its phonetic sign: the sign 'dog' signifies the physical dog, but in principle (if not possible in practise) we can have the sign 'xog' signify it instead.
Similarly, there appears to be no necessary connection between the physical sensation of the colour blue - its qualia - and its physical correlative, a certain wavelength of light. A video camera capable of 'false colouring' is sufficient to demonstrate this.
Given that there is no necessary connection; can we say that we have a theory of the colour blue? A theory of colour should be necessary, and not contingent.
Further, words do not stand by themselves in atomic isolation establishing no relationships with any others; for example the word (or signs) murder, morder, mourir, morbid and mortal show some affinity with each other. Similarly we do not the colour blue in isolation, our organic affinity with each other is the guarantee (with exceptions) that when I see the colour blue, a man in Borneo, or Papua New Guinea sees it too; or for that matter a vestal virgin in the Rome of Roman Antiquity.
This allows, possibly a test of the theory of the colour blue; at least in a kind of Gedanken-experiment.
Assuming that there is actually life elsewhere, which isn't a completely controversial proposition today, and for the purposes of this question, say on Mars; how can we guarantee that a Martian (unblemished and unflawed) who can see the same visible spectrum that we do (in principle easily determinable) actually see the same colour that we do?
I'd suggest that this test can serve at least as a falsifying test - is this right?