Chalk pastel colours.

Went down to an arts supplies store in the city today, and looked at chalk pastels. The chic working there was showing me them and there was quite a big range to look at. Single chalk were $1.70AUD each, a pack of twelve was $12 and a pack of 24 was $32. After that you start to go into the artists pastels, like, $60 for 30 when I would probably only use 10 or so. I haven't even begun weathering yet, but really need to jump into the ring. But I have hardly any idea what colours (of chalk pastels) I would be using for the corrosponding modeling subject. 

What colours would I use for armour and its specific weathering types?

 for aircraft and auto (if chalk pastel weathering really works for auto.)

Cheers Somenewguy!