QUESTION: "I love dark polishes, but they tend to leave stains on my nails. What can I do?" ANSWER: Try this DIY remedy: Soak nails for a few minutes in a solution of 1/2 cup lemon juice and 1/2 cup olive oil, suggests N.Y.C. manicurist Patricia Yankee. "The lemon juice gently lightens nails, and the olive oil moisturizes to help prevent stains." For really stubborn spots, N.Y.C. nail guru Jin Soon Choi recommends dabbing whitening toothpaste like Crest 3D White Vivid Toothpaste ($4; cvs.com) onto nail beds. "The whitening agents work on nails the same way they do on teeth," explains Choi. Rinse off the paste, then buff nails with a tool like the Dashing Diva Shine-On Buffer ($2; dashingdiva.com) or Revlon Shape-n-Buff ($4; drugstore.com) to remove the top layer of stains. In the future, always apply a base coat. "It's like armorit creates a barrier stains can't penetrate," says Yankee.