Can color film be used after it has expired? What are the consequences? How should it be preserved?

You can use it. Clarity will be slightly affected, depending on how long the validity period is. You'd better buy this movie now. If you want to keep it, it is recommended to wrap it in a sealed bag and freeze it in the refrigerator. Take it out in advance when using it. Don't open the sealed bag. You can use it in a day. Useless films can still be preserved like this.