Doing both things allows the maximum number of users to benefit. I'm pretty sure that's what you were getting at. The diff convention of marking inserted and

Doing both things allows the maximum number of users to benefit. I'm pretty sure that's what you were getting at. The diff convention of marking inserted and deleted lines by + and - provides a "channel" of info showing text comparisons. If the + lines were also blue-green and the - lines also red-violet then there's two channels conveying the same information. Using colors or not, we'd definitely keep the +/- markers. The highlighting methods are distinct, but line information is the same. The +/- notation will still be useful on a monochrome monitor or printed page. On a spiffy new 2500x1600 display, I'd personally prefer the color output to quickly find what's changed.