Tilapia isn't always perfectly white. It can look like yours does or it can even be slightly pink.
If you plan to freeze your fish from the market, ask the person at the fish counter to get a package for from their freezer supply behind the counter. As Uncle Bob said, much of the fish in grocery stores these days has been previously frozen.
Unless I'm going to eat my fish right away or in a day or two, I always ask for some that is already frozen. This advice came from my fishmonger.
"As a girl I had zero interest in the stove." - Julia Child
This is real inspiration. Look what Julia became!