Baking or Cooking - why orange and not other sweet citrus fruit? In most of the recipes that have any sweet citrus flavoring, it is usually Orange (zest and juice). In fact I've hardly seen a recipe that uses a substitute like mandarin, grapefruit, etc. Is there a reason why orange takes a preference and how easy is it to be substituted with another citrus? Lime and lemon of course are used a lot, but I'm referring to sweeter citrus fruit like orange, mandarin, grapefruit, etc. 

The reason for this question is that I was looking for an orange a month back and couldn't find it in any big supermarket. So, I bought a blood orange for its zest but luckily, after hours of looking, found one at a small grocer. So, if the situation comes up again, how do I know what to substitute the orange with? This is the recipe I wanted to make.
I don't claim that this is a canonical answer, but it seems to be a bit like the situation with apples. You have cooking apples and eating apples, which have been bred for different traits. Similarly you have juicing oranges, eating oranges, and bitter oranges (used for marmalade). The other citrus fruits which taste most like oranges (mandarins, clementines, tangarines) are more suited for division into segments, and you're more likely to see them used for decoration. You could juice them if you don't have a better option, but recipes will tend to use the most suitable commonly available option.

Grapefruit has a very different flavour, so you have to take that into account when substituting. It's also not necessarily sweet, and certainly I have never seen grapefruit sold as "sweet grapefruit" or "bitter grapefruit".