This is an idiom about intoxication;
'Rose' is one of the exceptions, see here http://french.about.com/od/grammar/a/adjectives_inv.htm
Thrissel.... but in this link rose is the Exception of the Exception..... French ha too much Exceptions!!!
Invariable French Adjectives Exceptions: 1) alezan (chestnut), fauve (tawny/fawn), incarnat (rosy), mauve, pourpre (crimson), rose (pink), and violet are variable according to the normal rules of agreement
in the exercise "des éléphants roses" is right.
I think that in this case it is clear it is plural because of "des". If there was just one pink elephant it would have been "Un éléphant". As a general tip, if something is singular and is preceded by "de" it would be whether "du" or "de la", and both sound different from "des". Same goes for "la, le" or "les".
The English word "rose" could be used as the name of a color but that is not what (Fr) rose means (Eng: pink). Either way, it must be placed after the noun using the BANGS rule. Adjectives of Beauty, Age, Number, Goodness/badness, and Size are placed before the noun; other adjectives go after the noun. Here's a tip: if it doesn't make sense, it's probably wrong.
Yes,there are pink elephants in the world.They are albino elephants
Sources: http://en.wikipedia.org/wiki/White_elephant_(animal) http://www.dailymail.co.uk/news/article-2121729/Pink-elephants-parade-makes-splash-Burmese-zoo-today.html https://www.google.com.my/search?q=real+pink+elephant&es_sm=93&biw=1366&bih=643&source=lnms&tbm=isch&sa=X&ei=4wqpVJOLHMqJuASq14HYCQ&ved=0CAgQ_AUoAQ
Chase them away! Chase them away! I am afraid! Need your aid! Pink elephants on parade!
Bonus points for anyone who got that reference. :3