Whether you should wash your hair before dyeing it depends on the situation and the advice given by the specific hair dye product you're using or by a professional stylist. Here are some general guidelines:

1. Clean Scalp: Some people recommend not washing your hair the day before coloring to allow natural oils to build up on your scalp, which can act as a barrier against irritation from chemicals in the dye. However, your hair should not be overly dirty or oily.
2. Product-Free Hair: If you've used styling products, it's generally a good idea to wash your hair to remove any residue that could interfere with the dye's adhesion.
3. Consult Instructions: Always read the instructions on your chosen hair dye product. Some brands might recommend washing your hair beforehand, while others suggest otherwise.
4. Professional Advice: If you're getting your hair dyed professionally, follow the stylist's advice. They will know what's best for the type of service you're receiving.
5. Personal Preference: Ultimately, it comes down to personal preference and the condition of your hair. If your scalp feels particularly dirty or irritated, you might want to wash it lightly before dying.

A common recommendation is to wash your hair 24-48 hours before coloring, avoiding any heavy conditioning treatments that might coat the hair and affect the dye's absorption. This allows your scalp to have a slight layer of oil for protection while ensuring the hair is clean enough for optimal dye absorption.

Always ensure that your hair is clean and free of excessive oils and products when you decide to dye it, and follow the instructions provided with the hair dye product or the advice of a professional.