When I play Candy Crush App on mobile there are 2 categories available for messages, one category which is represented by a trophy icon (which is where I found notice of orange candy challenge) and a second category represented by an envelope icon. When I play from Facebook on my PC, there is only the envelope icon available with no mention of the challenge. Also, a similar question to mine was posed a few months ago but the answer that was posted points user to a non-existent blog. See links below to view question/answer and the "missing" blog.
question/answer: https://care.king.com/en/candy-crush-saga/my-facebook-candy-crush-does-not-offer-the-challenges-for-gold-bars-how-do-i-get-it-to-appear
missing blog: https://care.king.com/en/blog/article/sugar-track-explained
