However, unknown to him, I suffer chronically from Smith's Disease, attacks of which are not obvious to another party; these attacks involve, among other things perhaps, the peculiarity that at the time red things look some quite different colour to me.

I know

that I have this disease, and I am having (and know that I am having) an attack at the moment.

In these circumstances I say,

"That pillar-box looks red to me". I would suggest that here the D-or-D condition is not fulfilled; my companion would receive my remark with just that mixture of puzzlement and scorn which would please my objector; and yet when he learnt about my attack of Smith's Disease, he would certainly think that what I had said had been false.