Tracking/displaying changes in documents

Question

Modern office products has a feature to track and highlight changes. Old versions of Miscrosoft Word used two colors (striked-out red for deleted and green for inserted text), while recent version changed highlighting style to one color (striked-out red for deleted and underlined red for inserted). As I can see Open Office uses only one color too. What might was the reason for this change of style to highlight difference?

I'm developing a web application with similar functionality. Using one color seems OK when there is small amount of changes, but it become ugly when there is a lot of changes. Highlighting with two color looks fine in both cases.

Answer 1

One issue that comes to mind is accessibility - with a non-negligible percent of color blind people, you have to add another distinction (the strike through and underline).

While one color might differentiate from the standard based simply on hue, differentiation more that that will be a challenge.

Don't forget that a lot of documents get printed in grey-scale, which renders multiple colors useless.

Answer 2

Accessibility, as Dan Barak said, not just for color-blindness (red/green is a big problem there) but also for reverse-video. Make sure that whatever colors you choose do not assume the default environment; for example, Word's yellow highlighter totally breaks in a reverse environment. If you're going to use color-coded text you're pretty much limited to the middle of the range of hues, where things will be visible on both light and dark backgrounds.

For additions, instead of underlining consider delimiting the text with brackets or boxing, along with use of change bars in the margin. (Strike-through for deletions still makes sense and does not conflict with web conventions.)