Full Idea
Block's Inverted Earth example (with matching inversion of both colours and colour-language) tries to show a variation of representational properties without a variation of phenomenal properties, so that the latter are not constituted by the former.
Gist of Idea
The Inverted Earth example shows that phenomenal properties are not representational
Source
report of Ned Block (Inverted Earth [1990]) by Mark Rowlands - Externalism Ch.7
Book Reference
Rowlands,Mark: 'Externalism' [Acumen 2003], p.132
A Reaction
(The example is actually quite complex). This type of argument - a thought experiment in which qualia are held steady while everything else varies, or vice versa - seems to be the only way that we can possibly get at an assessment of the role of qualia.