Colours, colour relationalism and the deliverances of introspection

Let colour relationalism be that form of colour realism according to which colours are constituted (partly) in terms of relations to subjects (possibly inter alia). Colour relationalism can be usefully contrasted with non-relationalist views according to which colours are, say, non-relational physical properties of objects (Byrne and Hilbert 2003; Tye 2000). One (historically important) way to bring out the conflict between these two sorts of views is to ask whether, in cases where subjects appear to disagree in the colours they ascribe to a common object, it must be the case that at most one of the ascriptions can be veridical. For example, suppose that you look at a ripe tomato, that it appears to be red and that you report as much when asked; and now suppose that an alien being, with very different perceptual apparatus, views the same ripe tomato, but that it appears to her to be green, and that she reports as much when asked. Would one of the two reports of the ripe tomato’s colour have to be mistaken, or is it possible that both of them could be correct? Anti-relationalist views about colour predict that, in such cases of perceptual variation with respect to colour, just as in the case where you and I disagree in (say) the shape we ascribe to an object, at most one report