So i created a simple visitor pattern for liquids. Such as Milk,juice and liquor.

a Milk class can look like this:

public class Milk implements Visitable{

public float tax=0;

@Override
public int price() {
    return 4;
}

@Override
public void accept(Visitor visitor) {
    visitor.visit(this);
}
}

//and likewise for juice and liquor

and then we can have a visitor which looks like this to do the work of calculating taxes :

public class TaxVisitor implements Visitor {

double taxPerentLiquor=.18;
double taxPerentMilk=.15;
double taxPerentJuice=.10;


@Override
public void visit(Liquor liquor) {

    int price =liquor.price();
    liquor.setTax((float) (price*taxPerentLiquor));
}

@Override
public void visit(Milk milk) {
    float price =milk.price();
    milk.setTax((float) (price*taxPerentMilk));


}

@Override
public void visit(Juice juice) {

    int price =juice.price();
    juice.setTax((float) (price*taxPerentJuice));

}

}

and when we are using it we would do this:

Visitor taxVisitor = new TaxVisitor();

    Milk milk = new Milk();
    Juice juice = new Juice();

    milk.accept(taxVisitor);
    juice.accept(taxVisitor);

and a "visitor" would calculate the tax for each liquid for me. and i see the benefit that i do not have to modify the collection of objects themselves when i want to add a new calculation. But my trouble comes when i want to add a new method. Following open closed principle i should not be adding new methods to the milk class for example. But let us imagine i want to add functionality to know what color the liquid is. So i'd like to extend the milk object to have a method called "getColor()" which would return "#FFFFFF". This seems like i would need a decorator pattern to add this functionality if i want to follow SOLID open closed principle. Is there a way to do this with visitor pattern ?