The best color for your loveseat will depend on the color scheme of the rest of your room. While soft neutrals are always a safe bet, you can use pastels or bold colors if it coordinates well with the rest of the room.
Since loveseats are small, they won't overwhelm a room if they're in a bold color, but they might end up competing with the sofa. If your sofa has an eye-catching design, get a loveseat in a more subdued color or pattern. If your sofa is a solid color like green, choose a floral loveseat with a hint of green to bring the room together.
Some colors hide dirt and stains better than others. Ivory and pastel colors will almost certainly require more cleaning and careful protection than black or navy. Families with pets and young children should stick to dark neutrals and jewel tones for all living room furniture.