"... need to add color with pastel chalk or other means..." Seems like more work than just ordering some Bragdon powders to me. And, I haven't found a color that they don't make to suit my weathering needs. But, that's just me.
Marlon
See pictures of the Clinton-Golden Valley RR
http://protoweathering.com/
Try these guys
I read a really good article in "Narrow Gauge And Short Line Gazette" about weathering with a product called Rottenstone. It is a fine limestone powder used to polish metal and furniture. He said you still need to add color with pastel chalk or other means and then brush on the rottenstone to tone things down and blend colors together. I was wondering if anyone out there has had any experience with rottenstone and how it came out? Did you like it?