I am a bit confused about it when sometimes it is shirt purple and other times it is purple shirt.
Colours always come after the noun in French, before the noun in English. If you have seen the colour before the noun in French, it will have been used figuratively.
"Gants" is masculine, so the adjective must agree with the noun, plural and masculine.
"des gants violets"
Again! There is CLEARLY no "V" sound at the beginning of violet on the slow play back.
There seems to be an inconsistent translation regarding the plural of colours in French, e.g. "des gants violets" in this exercise, but the previous translation talked about "des poches orange" Explanation, anyone?
You'll have to blame the inconsistency on the French language. Certain colors (often those from nature, but not all nature ones) are invariable and never form agreements with the subject.
Here are our Tips and Notes: https://forum.duolingo.com/comment/29997148
And a more comprehensive list here: https://www.thoughtco.com/french-adjective-of-color-1368982
I think it is about time you realised that in English we also say violet gloves, not always purple, that is more American. But you get marked wrong if you say violet instead of purple.