Both green and purple waterproof regular drywall can be used in bathrooms, depending on the level of moisture protection needed.   The regular green bathroom drywall is more resistant to water destruction than the purple one and should be used in areas where water is more likely to cause an issue. This includes showers, tubs, and areas near plumbing fixtures.   It's important to ensure that those regular drywalls are prepared with waterproofing materials in both cases. Otherwise, they won't be enough to protect your bathroom from deterioration.