Like lots of things in AC3D 5, ACMaterials are ACEntity.
So, if ACMaterial *m;
Code:
ACrgb rgb;
Float val;
ac_entity_get_rgb_value( (ACEntity *)m, "diffuse", &rgb );
ac_entity_get_rgb_value( (ACEntity *)m, "ambient", &rgb );
ac_entity_get_rgb_value( (ACEntity *)m, "specular", &rgb );
ac_entity_get_rgb_value( (ACEntity *)m, "emissive", &rgb );
ac_entity_get_float_value( (ACEntity *)m, "shininess", &val );
ac_entity_get_float_value( (ACEntity *)m, "transparency", &val );