Hi Alan,

Did he lose some fur? I have Siamese, and unless it's medical (which the
others will know more about) it could be one of several things. Firstly,
what colour is he? Many siamese darken with age, so this could be the cause
of the 'grayness' as the darkening is not as dark as the points, but a kind
of 'shading'. The other reason might be the fur loss; after losing fur
Siamese usually grow the replacement fur back darker. If he looks mottled or
patchy this would be why, and it will grow back normally after his next
seasonal moult. Now as for allergic reactions, I've never had any, but I
have modern Siamese which are slightly different to Traditionals. I have had
fur loss under stress, so look for any causes of stress, especially
territorial such as a neighbourhood cat terrorizing him through windows.
Check around your door and window frames for male cat spray (about 1ft from
the ground downwards); it smells metallic and glows under UV light. If there
is a spraying thing, either from him or outside from another cat, try
putting a door snake at the bottom of the offending door, and keeping him
away from offending windows until he settles down. Other allergies that
cause fur loss are detergents, flea allergy (quite common and even 1 flea
bite can set it off), floor cleaners, even room fresheners in some sensitive
cats. Have a look at his whole environment, and try and figure if anything
has changed, either stress-wise or allergen-wise. Anyway, I'm just throwing
ideas around. I don't know much about diabetes, but many of the others do
and I'm sure will have something of value to contribute. Best wishes for
your kitty :)