Brown mascara works well on brown eyes due to the principles of color theory and the natural harmony it creates. Here's why:

1. **Complementary Colors**: Brown eyes and brown mascara are analogous colors, meaning they are next to each other on the color wheel. This creates a harmonious and natural look, enhancing the beauty of brown eyes without overpowering them.

2. **Subtle Definition**: Brown mascara provides a softer look compared to black mascara. It adds definition to the lashes without making them look too harsh or dramatic. This is particularly beneficial for daytime or professional settings where a more natural look is preferred.

3. **Enhances Natural Tones**: Brown mascara can enhance the natural warm tones in brown eyes. Depending on the shade of brown used, it can bring out golden, amber, or even green undertones in the eyes.

4. **Versatility**: Brown mascara is versatile and can be used to create both subtle and dramatic looks. A single coat can add a natural enhancement to your lashes, while multiple coats can add volume and drama for a more intense look.

5. **Complements Skin Undertones**: Brown mascara often complements the warm undertones of the skin better than black mascara, especially for individuals with fair to medium skin tones. This can create a more cohesive and balanced overall look.

Remember, the key to choosing the right mascara is not just about matching your eye color, but also considering your skin tone, hair color, and the occasion.