I would submit that a grue detector isn't available. And that is the basic asymmetry that you seem to be missing.
For example, if I measure a piece of wood and find that it is 1 meter today, and 1 meter yesterday, and 1 meter the day before that, the natural deduction, assuming no outside intervention, is that it will be 1 meter tomorrow. There are measuring rods that will detect '1 meter long', but none that will detect '1 meter long until today and 2 meters long until tomorrow' as a basic measurement. So the grue analogy fails for distances.
But green is *actually* simply light with a certain wavelength--a distance. That reduces the color green to a basic measurement of a distance. There is no basic distance of '520 nm until 2018 AD and 400 nm after that'. So grue is not a 'natural' color. It is a contrived color for philosophers only.
Furthermore, since there is no natural 'grue detector', the aliens will not and cannot naturally default to grue. The emeralds keep the same spectrum of wavelengths hroughout. They don't change from a 'grue wavelength' to a 'bleen wavelength' because neither is well-defined.
Again, the only thing that you are showing is that
you completely misunderstand the argument!
Let me explain it to you as simply as I can from the beginning. Goodman's argument is this:
P1. Induction ONLY WORKS when we are dealing with law-like properties.
Example: If we say "This icicle is cold. The last icicle I felt was cold. Therefore, the next icicle I feel will be cold." then most people would agree. Cold seems to be a law-like property. On the other hand if we say "The woman I see is wearing glasses. The last woman I saw was wearing glasses. Therefore, the next woman I see will be wearing glasses." then most people would disagree. Women and glasses don't seem to be a law-like property.
P2. We cannot tell when the property we are describing is a law-like one and when it is not.
Conclusion: We can never know whether induction is going to work.
So premise 1 is uncontroversial. The conclusion follows from the premises. Accordingly, what Goodman needs to do is to convince us that premise 2 is true, and he does this by using the Grue Thought Experiment.
Imagine that someone sees an emerald and says, "This emerald is grue. The last emerald I saw was grue. Therefore, the next emerald I see will be grue." Most people would not agree that grue is a predictable predicate of emeralds. Few people believe that emeralds are suddenly going to emit bluish light after AD3000. Green, on the other hand, does seem to people to be a predictable predicate.
Why is this? Why is green law-like whereas grue is not? Goodman argues that this is because of entrenchment. Basically we are used to using words such as green and blue whereas we are not used to using words such as grue and bleen.
Now YOUR ARGUMENT against this is to say that distance is a law-like predictable predicate of wavelength. This answer, however, is
begging the question. Goodman has challenged you to provide a
general rule that will let you distinguish between predictable predicates and non-predictable ones. Simply claiming that distance falls in the former category is
not a general rule that we can apply to all future situations thus ensuring that we will always know when induction will be reliable and when it will not be.
Furthermore, your claim that the wavelength is a certain distance and always has been is false. An emerald under blue light will reflect a different wavelength light than will an emerald under red light. Accordingly a person who uses adjectives such as greena and browna will confidently be able to say that the emerald he is looking at is either greena or browna just by looking at it whereas a person who uses adjectives such as green and brown will need to first determine what light is shining on the object in question before he can determine whether the object is green or brown.
So although some people might argue that grue is a bad adjective because you have to have a calendar on hand to determine what some color is, the greena and browna people would make the same argument against us. Just as grue requires external knowledge to determine whether something is grue, so too green requires external knowledge to determine whether something is green.