The correct definition of Nelson Goodman's famous predicate grue has been the subject of some controversy. Goodman's original definition is somewhat difficult to find online because most people do not quote Goodman verbatim, but instead offer their own paraphrase. Below are exact quotations from Goodman's book Fact, Fiction, and Forecast. Differences in different editions are noted (however, I have not managed to get a copy of the 3rd edition yet). I give, in addition to the definition of grue, the definition of other related words. I believe it is clear that under Goodman's definition, emeralds do not change color, but you can judge for yourself.
Chapter III, section 4: It is the predicate "grue" and it applies to all things examined before t just in case they are green but to other things just in case they are blue. Then at time t we have, for each evidence statement asserting that a given emerald is green, a parallel evidence statement asserting that that emerald is grue. And the statements that emerald a is grue, that emerald b is grue, and so on, will each confirm the general hypothesis that all emeralds are grue. Thus according to our definition, the prediction is that all emeralds subsequently examined will be green and the prediction that all will be grue are alike confirmed by evidence statements describing the same observations. But if an emerald subsequently examined is grue, it is blue and hence not green.
Consider...the predicate `bleen' that applies to emeralds examined before time t just in case they are blue and to other emeralds just in case they are green.
Let "emerose" apply just to emeralds examined before time t, and to roses examined later.
Chapter IV, section 4: Suppose that the predicate "grund" applies just to all things examined up to a certain time t that are green and to all things not so examined that are round. [Note: The word "just" was omitted in the 2nd edition, and "Suppose that" was changed to "Suppose, however," in the 4th edition.] Footnote [omitted in 4th edition]: "All emeralds are grund" is not, it must be remembered, equivalent to "All emeralds are green and round." All emeralds may be grund without all being green, without all being round, and even without any emerald being both green and round.
A thing is grare if either green and examined before t, or not so examined and square. [4th edition only]
Let the predicate "emeruby" apply to emeralds examined for color before t and to rubies not examined before t.