If you are in the pink, you are fit, healthy, and happy.

For example:

He looks in the pink after his vacation.

She’s been working out regularly and is now in the pink.

After recovering from the flu, he’s finally back in the pink. 

Good to see you in the pink again, John. You looked like death last time I saw you!

Tradução:

“In the pink” significa estar em boa saúde, feliz e em excelente condição física.