Can I sacrifice a treasure for mana not in my commanders colours?
As the rule states:


  A card's color identity is its colour plus the color of any mana
  symbols in the card's rules text.


Flash Conscription's rules text contains a white mana symbol, therefore it it's colour identity is Red/White.

The only time this does not apply is when that symbol is included in reminder text e.g. Extort like on Crypt Ghast

it should also be noted:


  903.4c The back face of a double-faced card (see rule 711) is included when determining a card's color identity.


so Elbrus, the Binding Blade / Withengar Unbound from is classed as a black card because the back face has the black colour identifier on it's type line.

Also split cards like those with fuse mechanic or aftermath also take the colour identity from both halves combined.

As for generating mana outside of your commanders colour identity, this is fine and allowed in commander rules, as of January 2016