Thank you. I fine.
I believe they are for fun. I only remember for each day it's different colour like rainbow from Mon to Sun.
So Red, Orange, Yellow, Green, Blue, Indigo, Violet.
I couldn't even remember who started it. LOL..but there's nothing that can stop me searching on steemit for answer. Here's it:
https://steemit.com/colorchallenge/@kalemandra/new-colorchallenge-for-all-steemians
Apparent many including myself have not strictly follow the rules, e.g., title and first tag #colorchallenge , one photo (art/photo) - does not say any restriction besides that.
Easiest way I figure to remember the day is by the rainbow colours.