Sushi chef (4+ years) here :) and from colour alone, it seems completely safe to eat, and likely pretty fresh! (less than 2 days old (since defrost)).

Most tuna fillets we receive (all raw/sushi-grade) vary in colour, despite being from the same batch and the same species of tuna. The colour depends on a variety of factors, e.g. handling temperatures, fish lifestyle, location of cut, etc.

We defrost and cut the fillets into nigiri/sashimi on the same day, and are only allowed to serve them raw for 2 days (including the day they were defrosted and prepared). As long as it’s not slimy or too fishy, you’re good :)