If we're limiting ourselves to deductive reasoning, then yes – the facts as stated do not give enough information to deduce that Greg must be white.
If instead we use abductive inference, we might seek the simplest and most likely explanation given our universe of observations. Sherlock Holmes was a big fan of abduction!
Much of real-world reasoning is abductive to a greater or lesser extent. There is a well-known joke about some motley band of engineers, logicians, mathematicians, statisticians, etc etc catching a train through the Highlands. They see a black sheep, the engineer says "look, all sheep in Scotland are black!", the statistician says "no, you can't say that – just that MOST sheep in Scotland are black", another says "no, we can only say that at least ONE sheep is black", another says "no, it's only black on at least one side", then the one you're stuck next to at the party says "you're all wrong, we can only say that at least one sheep in Scotland is black on at least one side at least some of the time". The last statement is fully deductive; the rest of them are abductive, and more-or-less useful.
If instead we use abductive inference, we might seek the simplest and most likely explanation given our universe of observations. Sherlock Holmes was a big fan of abduction!
Much of real-world reasoning is abductive to a greater or lesser extent. There is a well-known joke about some motley band of engineers, logicians, mathematicians, statisticians, etc etc catching a train through the Highlands. They see a black sheep, the engineer says "look, all sheep in Scotland are black!", the statistician says "no, you can't say that – just that MOST sheep in Scotland are black", another says "no, we can only say that at least ONE sheep is black", another says "no, it's only black on at least one side", then the one you're stuck next to at the party says "you're all wrong, we can only say that at least one sheep in Scotland is black on at least one side at least some of the time". The last statement is fully deductive; the rest of them are abductive, and more-or-less useful.