Magick itself doesn't have any colour,but to specify magick done with light energies such as angels, light deities etc is considered to be white magick and in layman terms,people consider white magick done for the purpose of positive intentions (which is wrong because even white magick can be done to harm someone) while black magick is magick done with dark energies such as kali maa, demons etc to manifest a specific goal and in layman terms,some people consider black magick as magick done to harm someone(which is totally wrong because even black magick can be used to heal or harm someone)

No, just like any other spiritual work,it depends upon a lot of factors such as how much a client is detached, whether it is meant to be or not,what is the mindset of the client and whether spirits agree with your request or not.