Colour filters are something that many astronomers will agree to disagree on with regards their effectiveness on bringing out certain features on Planets.
So I can only go on what I have seen myself through my own telescope and not what others think. In my opinion the #56 green filter is perfect for making polar ice caps on Mars stand out..When looking through my 6″ dobsonian I could only just make out what I thought was the southern polar ice caps. With the #56 green filter attached the ice caps “jumped out” and were so much more clear against the rest on the Planets disc. No whether it was enhancing the white of the caps or reducing brightness from the the red and green areas, making the white features stand out more, I am not sure. What I do know is that it had the desired effect
Available in 1.25″. Screws directly into any compatible eyepiece