Can I substitute red wine vinegar for white wine vinegar when preparing a vinaigrette with grilled salmon?
You can add any kind if vinegar you'd like, that's a matter of taste, as long as you add an equal quantity. White wine (and white wine vinegar) usually goes better with light foods like fish, but there will be no impact on how the vinaigrette will come together if you use red wine vinegar.
Sure if you dont mind the sauce being a little pink?
Depends on what flavours exactly you are going for. Red vinegar does tend to be less sharp / strong than white spirit vinegar.
The distinction in flavours will probably be subtle enough as to not matter too much but still it will make some difference.