There's an official term in knitting that I should probably explain a little bit before I start talking about sister-socks.
The official term I am referring to is "fraternal socks" or a "fraternal pair". These are socks that have two colours, but in the second colour, the main and contrast colour are switched. That way, the socks are definitely a pair -- knit in the same colours and from the same pattern -- but they are also a little bit different.
Examples of fraternal pairs I knit:
In most cases, you can only tell they are a fraternal pair because the toes are a different colour. The main "body" of the sock looks almost identical to a casual observer. Of course, a knitter will claim your leg and start analysing the pattern and how it works for the different colours, but they are a bit special, after all.
Some knitters feel the need to knit most of their two-coloured socks as a fraternal pair. Either they find it too distracting to have a simple pair where both socks are exactly the same, or they want to even out their yarn usage which can be handy if one colour is used more than the other. Instead of using 40 grams of one colour and 20 grams of the other, you'd use 30 grams of each and the remaining skeins are of equal size.
I can understand the need for having similar-weighing skeins left over, but it doesn't really matter because after knitting 10 pairs of socks your remnant pile is going to be out of control no matter what you do.
I've coined a phrase that I don't think existed yet. It's hard to verify if there's an official term for it anyway, because only people who knit socks would talk about it. If I Google for it, I can find rules for military personell for wearing two socks of different colours, or how to match your socks to your suit. But nothing about what I am talking about.
The phrase I've used is "sister-socks". It's when I knit several socks with the same main colour, but use different colour contrasts to offset the yarn.
Examples:
The fun thing about sister-socks is that you can select any colour from a multi-coloured yarn, and knit the heel, cuff and toes in this colour. And because you choose a different colour to "lift up", the results can be quite striking. It always amazes me to see how different the sock looks with another contrast colour.
Of course, the bottom pair, with orange and blue contrasts, are Eisirt's socks. He's a quirky man. He wears one sock with a blue toe and one sock with an orange toe because I gave him BOTH of these pairs to wear. So he refuses to wear them as a true pair. He mixes them up as soon as they come from the washing machine.
I am going to throw him a curveball... I have enough of this yarn left to knit one more pair, and I've got a purple skein to do the contrasts with. He can mix it up EVEN more. One orange and blue. One blue and purple. One purple and orange. He probably will, too.
Triplet-socks.