I knit a lot of these Fair-Isle socks. I just make up the patterns as I go along. Basically each stripe is 5 rows, with the 3 middle rows containing the pattern. In general I try to use small pattern repeats of 4 or 6 stiches, a few are more complicated. In the heel and toe I just use plain stripes so that the patterns don’t get broken up by the decreases. Also, I find that doing Fair-Isle in the ankle area sometimes makes them too tight to get on and off.
If you look closely you’ll see that the 2 socks are similar, but not identical. I think that adds to the fun and makes then a touch more whimsical.
At some point, when I started to make socks I bought about 20 colors of basic sock yarn to start a “sock stash”. Now, when I knit a pair of socks I just use whatever I have in the stash. Every now and then I’ll pick up the odd skein or 2 if I see a color that I don’t have. This is a great idea for using up whatever leftovers you have from knitting other socks.