What are discord colors?
Colours that clash, don't go together
Discord basically means there is no harmony. If something has discord, it isn't going well, and is much chaos. If you've seen the character discord from My Little Pony Friendship is Magic, he demonstrates the meaning very well (Discord can be seen in S2E1&2-Return of the elements of harmony, and S3E10-Keep Calm and Flutter On)
Fluttershy met discord at the same time as all the other 5 "mane" ponies in the season 2 opener "The Return of Harmony part 1." Discord was in part 2 as well when they defeat him. In season 3, episode 10 "Keep Calm and Flutter On," Discord returns where he stays with fluttershy. Discord again makes several appearances throughout season 4.