How do these people choose their colours?

https://preview.redd.it/1edaykwxveoe1.jpg?width=209&format=pjpg&auto=webp&s=f3cb977a778a9cfc70511423b2c144d1185983c9

https://preview.redd.it/ohx04pwxveoe1.jpg?width=222&format=pjpg&auto=webp&s=adee82c0fa25126bd76efb2c273c4d7aeab89004

https://preview.redd.it/5g9zhswxveoe1.jpg?width=229&format=pjpg&auto=webp&s=5c525cbcbba1fd7a0deddb5a4891bd60d0f364ff

https://preview.redd.it/4ivn2lwxveoe1.jpg?width=238&format=pjpg&auto=webp&s=7bd30571352235b821a698e05c794825d058aa0d

https://preview.redd.it/fdk0slwxveoe1.jpg?width=229&format=pjpg&auto=webp&s=801514c5aab0c882a72ec37e0ed1123fa02fefa0

https://preview.redd.it/pubihnwxveoe1.jpg?width=252&format=pjpg&auto=webp&s=fec631cb3d8c0f72fa9596fad9f31ec66ad6d3cc

I always see people with these really pretty colors on their ponies. Does anyone know how they pick their colors? Any tips on how to use colors like them? Specifically hue shifting and saturation