Good to know. Are there any sources for a good lighter shade blue? Right now I use Child's which is darker. Also a lighter blue kersey?
Good question. I know Ben Tart is selling blue flannel for sack coat purposes, and blue flannel can be found for sale in quite a few fabric stores and online. I really don't know where to find a lighter shade, though. As far as kersey goes, I think Jarnagin's is pretty light, though I haven't seen it in person in awhile, so I can't comment on its authenticity. You might also ask for swatches from Chris Sullivan. He sells all wool and wool blend kersey from Woolrich.
I wish I could help more, but I haven't made any Federal garments in the past. I am planning on making a few here in the near future, though, and so I will be purchasing blue flannel and sky blue kersey at some point.