Ash grey ceramic can be used in exterior applications in very humid climates as long as it is a high-quality ceramic tile that is specifically designed for outdoor use. Ceramic tiles are known for their durability and resistance to moisture, making them suitable for humid environments. However, it is important to ensure that the ceramic tile has a low water absorption rate and is frost-proof to withstand extreme weather conditions. Additionally, proper installation techniques and maintenance practices should be followed to ensure the longevity of the ceramic tiles in humid conditions.