You Are About to Enter Draftland
[ ] Black headlines on a white background
[ ] Colored headlines on a white background
Answer: Black headlines on a white background
Notes and assumptions....
This particular Q&A is more about defaults than about black-and-white [pun intended] rules.
The default since Gutenberg has been black ink on whatever substrate you had in hand: parchment, rag paper (just like the ancient Egyptians made), and later clean flat white paper when you had it. Modern newsprint didn't come along until 1844 when Canadian inventor, Charles Fenerty, invented wood-pulp paper. He didn't take out a patent. Not many "saw" what Charles Fenerty discovered. But in fact the man's invention established an entirely new industry, once people started to get it.
Of course, pray when there's a new industry.
That it does as much good as it can & as little harm as it necessary. No free lunches.
Black ink will be your default. Which means: anything other than black ink needs a second thought. Colin Wheildon told me so. Colored headlines, his studies found, reduced easy skimming. And "easy skimming" is the highest value we aspire to in donor communications. "Easy skimming" is what "streamlining" was to earlier generations;;;in our full-message-assaulted culture;;;going down for the final count culture