Good catch. That is the Greek question mark. I think you'll find mention of it in one of the Tips and Notes. I"ll check it's a good idea to include it.
Thanks for the info!!
There is a semi colon instead of a question mark
The semi colon is the Greek question mark.
Is it your orange hat?
Is this also correct?
Not really... Here, the question is about whether the hat is orange or not.
What difference in emphasis is there between Είναι το καπέλο σου πορτοκαλί ; and Το καπέλο σου είναι πορτοκαλί ; ?
None, unless you emphasized it when speaking. In Greek as long as you have the right part of speech you can very often change the word order...but not always. So, keep asking we're here to answer.