You can use the tint effect for this... the trick for a smooth transition is to probably use something like LERP.
First, apply the tint effect to your object, then choose the RGB or HEX value you want your tint to be.
Last make an event to smoothly change the tint... something like (pseudo-code);
-- Set tint value to: lerp(self/tint.value, desired(tint).value, 1-0.3^dt) - (change the 0.3 to 0.1 or even 0.01 for a super fast change or lower it to like 0.5 or even 0.99 for a slow or super slow one)
The same will apply to go back to the other colour... just do another lerp action from the self/tint.value to the desired(no tint).value