My sister's dog is all black so as you can imagine, it is almost impossible to see in the park when she walks him on these dark winter nights. That's why I made this from glow in the dark cord. It isn't paracord (although you can get GID paracord), it's a bit thicker at 4.76mm (ideal for a dog collar) and I got it from Ebay for about £5 for 15 metres. I have loads left over so I may use that to make a knotted toy for him (monkey's fist).
The knot used is called the cobra weave. There are LOADS of tutorials on making cobra weave paracord bracelets, some using two colours.
Since a dog collar is bigger than a bracelet, I obviously had to estimate the right amount of cord. Based on the suggestion of using 14 inches of cord per inch of required "bracelet" I used 210 inches and had about 24" remaining to trim off. With this kind of thing it's better to have too much and trim off than to run short.