I usually use a mix of codex grey and white to create a light-grey basecoat. Starting from there I add more white to the mix and shade the NMM effect until it is almost white. After that I highlight the edges with pure white.
Hi chaosfreaks,
By no means do I claim to have mastered this technique. For a silver basecolor I like to mix a tiny amount (not too much) of GW Sky blue to Codex grey and then add a little Chaos Black to darken it a little, now just add more and more white to the basecolor for your highlights.