Translation:Are Klingons blue?
People often bring up ao meaning both blue and green in Japanese but in practice when people are not using language poetically, there is a VERY strong tendency for them to express green as midori and blue as ao. I have never had a case where I have wondered which color a Japanese person was talking about because of this. I read a paper that makes a strong argument that there are linguistic reasons ao is sometimes used instead of midori not because they didn't make a distinction between blue/green.
It is true that in modern Japanese, 青い is the basic everyday word for "blue" and 緑 is the basic everyday word for "green", but there are still some contexts 青い is used for "green", including for traffic lights (red, yellow and "blue") or some place-names (like 青山). I don't have much first-hand experience, but I understand that in rural Japan, 青い is used more often for "green" than in Tokyo. In fact, it was once explained to me that in the dialect of Japanese spoken in the Tohoku region, 青い even includes some shades of yellow (like SuD in Klingon!).
SuD can mean blue, green or yellow depending on context (kinda like how the Japanese word 青い can also mean "blue" or "green").
However, as explained in Klingon for the Galactic Traveler, page 82, if you want/need greater specificity, you can use SuDqu' for "green" and either SuD 'ej wov or SuD 'ach wov for "yellowish".
You can also use SuD 'ej XXX rur where XXX is an object, to indicate the colour of that object. For example, I would think that SuD 'ej chal rur would mean something like "sky blue", whilst SuD 'ej jul rur could mean "bright yellow (like the sun)".
So the sun IS yellow on Kronos, then? I was wondering if the metaphor, if you will, for yellow in Klingon would utilize the word for sun, or if maybe the Kronosian sun was actually red, or some other color altogether.
Kind of ironic, isn't it, that Klingon considers the sun - something usually associated with warmth and heat - to be SuD, a "cool" color, rather than Doq, a warm one! :-)
Note that Micheal is speculating in his color references, not quoting canon (though the method of making color references is canon). Most likely he is talking about color references that you can use on earth while talking to humans in Klingon. I don't think we have any evidence of what color the sun of Qo'noS is or appears to be.
Think of SuD instead as meaning "cool colored" and Doq as meaning "warm colored". It may be an unusual division between warm and cool, but it might help to think of it in this way. So it's not that SuD sometimes means "blue", sometimes means "green", and sometimes means "yellow". It's that it always means "cool colored" and those are the cool colors for a Klingon. If you want to be more specific in Klingon there are ways to be more specific, but that's not what we're learning right here. English doesn't really have a word for cool colored, so to translate into English pick one of the cool colors. Duolingo will accept any of the cool colors for SuD. Use "blue", use "green", or use "yellow" - they are all accepted, even though SuD is more general than any of those.