Silver toners work in a similar way to white toners only they are blue based rather than violet based. It cancels out the yellowness in the hair but also dyes it a very very pale shade of blue to give it a silvery look.
Since toners are like a very weak dye, they will only work on very light hair. If your hair isn't light enough not much will happen.
There are a number of white and silver toners around. The easiest to use are the ones made by the same companies that make unnatural coloured dyes. LaRiché Directions makes both white and silver toners and this is applied like any other semi-permanent. You can leave it on your hair for a few hours but one hour is usually plenty. Special Effects make an excellent white toner (the best I've tried) but be careful to follow the development time as it has a tendency to colour the hair violet. Other toners come in liquid form and can be applied by dabbing it onto the hair using cotton buds. Be careful as these are often setting lotions as well as toners.
.... schwartzkopf Igora Royal to make quite a strong silver. You can buy this at beauty supply shops but be aware that you buy the colour and the developer separately. The correct mixture for silver (and not the blue that his hair was first coloured) is 6 parts "platinum" and 1 part "anti-orange concentrate". I mixed that with 30 volume peroxide though you can use 10 or 20 volume if your hair is weak. This will produce a very pale silvery white colour.
And you can always use a silver shampoo to get rid of the yellow tones.
R...grey hair can be ugly if its growing out surrounded by yellow tones. I would suggest doing some treatments to "wash out" the yellows and maybe even give it an all over silver tone. That, to me, looks better than grey-yellow hair or salt and pepper. The above was copied. I have not tried it myself.