My snowflake (who I've had for almost 2 years now) also went into a "hibernation" mode for about 2-3 months, where he would only eat about once a week, and eat very little when he does. His activity was also a lot less, though I didn't notice any changes in his color.
But out of the blue and for whatever reason, he suddenly woke up and seems back to his normal self again (appetite and activity). I can recommend patience, and try mixing up his meal variety until he bites more. Mine won't touch silversides anymore, but loves to feast on krill!