If summoned by weather, weather ball turns into the type that the weather is. For example, if you set rain first then set sun, weather ball would be fire as it still would be sunny. The field probably says, "The attack was rainbow charged", because weather ball is still "normal" type to the battle screen.
Abilities like chlorophyll still work if the weather is the one needed. If sun was set first and rain was set second, then abilities like swift swim would proc and etc.