Create, copy & paste into Yahoo Mail

Hello,
I tend to write somewhat complex responses to friends that apart from including bold & italics and possibly images, I also insert my response to a phrase of theirs directly below it in a different color (no color change option here, or did I miss it?).

I'd prefer to take my time and do this offline using Word or somesuch, but then copying and pasting it into Yahoo Mail removes all my lovely taradiddles, y'know?

So, apart from using the "Offline" feature, as it may be days before I send it, how can I retain my formatting when pasting it into Yahoo Mail, or even Gmail for that matter?

TIA
fsw