Colors in html emails work best as a six character hex ('#ffffff') rather than '#fff' or 'white'. See nex3/sass#343 for details.
Somewhat unfortunately, sass will convert '#ffffff' to 'white'. When premailer inlines css generated by sass, it will insert 'white' instead of '#ffffff'.
nex3/sass#343 goes over the sass issue. I believe sass's position is correct by saying this is something that should be fixed in premailer.
Examples of how html email can be broken by using 'white' or '#fff':
Some browsers and email clients have trouble with 3-character hex codes:
https://litmus.com/blog/background-colors-html-email
We can help by making sure that any 3-character hex code is turned into the 6-character equivalent.
See this issue in the premailer/premailer repo: https://github.com/premailer/premailer/issues/109