Thanks for that explanation! So if the German aligns with Danish in this case, it would mean two separate colors, which is different from how we would express it in English. In English, blue-green would mean a color which is between blue and green, a blending of the two. If there are two separate colors, blue and green, then we have to use "and." A blue-green shirt is one color, a blend of blue and green. A blue and green shirt has two distinct colors, blue and green.
In Italian it's used extensively to call soccer teams (mostly non-hyphenated): rossoneri (Milan), bianconeri (Juventus, Udinese), bianco-azzurri/biancocelesti (Lazio), giallorossi (Roma), nerazzurri (Inter, Atalanta), rosanero (Palermo)... and obviously the azzurri, even if it's just one colour.
That is a very good question, because it would indeed make a difference in how we express it in English. If two separate colors, we would need to use the "green and white" construction. A green and white shirt has two distinct colors, green and white.
If two blended colors, we would say "greenish white" or "greenish-white," which would mean white with a tinge of green. If it were green with a tinge of white, we would say, "whitish-green" or even "milky green."
With two colors which are between one another on the continuum, we could also use the "ish" form, as in "reddish orange."
Sometimes we think of an intermediate hue as a color on its own, perhaps, as geekns remarks below, because of Crayola crayons! In those cases, we often say "blue-green" or "red-orange," but "green-white" is not one of those cases (at least in American English). That's probably why some of us are uncertain whether this phrase is trying to convey two separate colors or one blended color. (Maybe that's because white and black aren't really on the color wheel, so we can't say they are in between other colors, but they can be mixed with and influence other colors, lightening or darkening them... or be influenced by other colors, as in "purplish black.")
I cannot find anywhere else that has hyphenated colors or discusses them! Except PONS has a phrase for "green-white mottled". http://en.pons.com/translate?q=gr%C3%BCn-wei%C3%9Fesl=deenin=lf=de
In English colors that are hyphenated or joined into one word are a color that is mixed between two colors. Wikipedia says that the two colors are equally mixed, so i'm guessing this is a light green? But it doesn't match the charts here: http://german.about.com/library/blfarben_voc2.htm
I grew up thinking of colors in terms of Crayola Crayons. Their "Green-blue" is a dark blue with a little green added, and "Blue-green" is very slightly darker and greener than what i would call turquoise (which i know some consider to be a green, the blues and greens in particular are very subjective in this way). So if i was trying to find a specific crayon by Crayola's rules (that the second color predominates) then i would look for a green so light that it would almost be white, like an iced mint. Their "Sea Foam Green" and "Magic Mint" come to mind.
Does anyone have a resource about what Germans think on the subject, or if their is one school of thought (as i have just demonstrated, Americans have at least two!).