I'm not sure this has _ANY_ basis but our vet reckons that Rubies are the hardiest out of the four colourings. In his experience he says he's seen more elderly rubies that don't pick up illnesses as easily as the other 3. He put black and tans next and tris at the bottom (sorry! ). I've never heard this before and I'm sure there are millions of exceptions but has anybody heard the like before?