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I once read an article arguing that red and green are bad choices for diff, because
However, I cannot remember where I found that article and which alternative colors were suggested.
What would be sensible alternative colors for red/green?
Red and green has a certain logic to it, in the sense that Western culture does associate green with “positive” states and red with “negative” states. In this sense, red is appropriate for deleted code because it is believed to be less correct than the replaced code (otherwise, it wouldn’t have been deleted; remember the teacher’s red marks on your paper). Deleted code is also negative in the sense that it isn’t run –it’s “stopped,” while the (green) replacement code “goes.” (without the original article I can’t judge the merits of its argument; maybe someone was traumatize by an over-zealous teacher).
However, the accessibility (color-blindness) concerns are legitimate. The usual ways of dealing with this, assuming color coding is the right choice in the first place, is to add a redundant code.
You could, for example, and add strikethrough to make it clear what’s deleted:
However, that also makes the deleted text harder to read, so if the task involves really studying the deleted text, it’s not a good choice.
A common choice is to go with shade coding. With a white background, you can go with a very dark green (okay, almost black) and keep all text minimally legible (and nonpink):
The above shades contrast 3.0 against each other and at least 4.5 with the background, which is the minimum you want, and also about the most you can get.
The deleted text will appear lighter than the replacement text, helpful to not only those who are color blind but also for those who use non-color printouts (the default at my work). It seems sensible for deleted code to be lighter, as if it isn’t there as much as the replacement text.
If for any reason you want to avoid negative/positive connotations, I’d recommend a brown-blue combination:
These have no particular strong associations in Western culture, and blue-yellow color blindness (and total color blindness) is much rarer than red-green, so more people will benefit from the color coding. I also made the deleted code a lighter shade than the replacement to have shade coding too.
The direct answer to your question is completely opinion based, so I'll ignore it. Instead...
To arbitrarily pick two different colors would go against a well established standard. By not maintaining consistency with those standards you increase the learning requirements of your application and increase the potential for confusion. Which makes doing such a thing a really bad idea.
"Because color blindness" is a reason often provided by people who do not understand color blindness. Color blindness...
While it is important to take such conditions into consideration, it is important to understand how such conditions work.
Red does not imply bad, nor does green imply good. You can't just take a color's meaning from one context and and move it to another.
So... What are good colors for deleted and added code in a diff program? Red and green, respectively, with a user option to change it.
Short, practical answer (since I was asked about it in a comment):
Open ~/.gitconfig and add
[color "diff"]
old = yellow
new = blue
See git --help config for details.
Go to your profile preferences and scroll down to Diff colors. You can select between yellow, blue, red and green or enter your own color.
¯\(ツ)/¯