This is a question that involves a reference to both the breed standard and cat anatomy. We know that kittens have blue eyes and that eye colour develops. This is because of the development of pigmentation. Blue eyes lack pigmentation because the colour blue comes from refraction of the light rays not the pigmentation in the iris. Initially it is not possible to know what color the eyes will be unless someone knows better than me.
So this Siamese cat appears to be developing green eyes from the initial ‘kitten blue’. That is normal anatomically. However, from a cat breed standpoint it is not good news on the face of it.
The Cat Fanciers’ Association breed standard for chocolate point Siamese cats for the eyes is:
Eyes: almond shaped. Medium size. Neither protruding not recessed. Slanted towards the nose in harmony with lines of wedge and ears. Uncrossed….Eye color: deep vivid blue.
For a Siamese cat to be a true Siamese cat of quality from the perspective of a cat breeder and the cat associations he/she must have deep blue eyes. Therefore it may be the case that the cat the question is not a purebred Siamese. I am guessing because the eyes may well turn blue at the end of the day after several more months. Also the cat’s owner refers to ‘look green’. They may be undeveloped blue.
P.S. Sorry I don’t have a picture of the cat in question.