What two colors make silver?The bad news: If you're wanting to use 'ordinary' colors to mix a silver that is shiny and reflects, you can't. You need a metallic pigment. My favorite is Liquid Mirror produced by Tri-Art (Buy Direct). It's not cheap, but it sure is shiny!
The good news: If you want to mix a color that will make an object look like it's silver, and paint reflections and highlights onto this as if it were a reflective surface, then you're after mixing greys, which you can do. Everyone has their own recipe grey; I like to mix titanium white, Prussian blue, and burnt umber. Use a small viewfinder to help you identify the tone of grey you need. Get the tones right, and it'll look like a silver object.
Practise Tone by Painting a Gray Scale
What's Payne's Grey?