Full Idea
It is impossible to form the concept of 'chromatic colour' by discriminative attention to a feature given in my visual experience. In seeing a red window-pane, I do not have two sensations, one of redness and one of chromatic colour.
Clarification
'Chromatic colours' are all those apart from greyscales
Gist of Idea
We can form two different abstract concepts that apply to a single unified experience
Source
Peter Geach (Mental Acts: their content and their objects [1957], §10)
Book Reference
Geach,Peter: 'Mental Acts: Their content and their objects' [RKP 1971], p.37
A Reaction
Again Geach begs the question, because abstractionists claim that you can focus on two different 'aspects' of the one experience, as that it is a 'window', or it is 'red', or it is not a wall, or it is not monochrome.