Do not harm, but good. Wish not bad things to come, but good onto them.
Ex: someone does you wrong, is unkind, rude, or whatever the case. Wish not evil or bad things to happen to them. Instead wish happyness, for them to learn kindness, honesty, or that which suits the time.
If it is truely in their nature to do harm and be bad, then this in itself would cause them pain. If they are capable of changing, then they will change to the suggestion put forth of your actions. And if you believe in karma, 3fold rule, or the such, then since you're putting positive/good thoughts out, you will get positive/good back.
Try this, go up to some random person on the street, in your work, school, or where ever and smile at the, be polite to them, or any other nice thing. More then likely you will get a positive feedback from them(unless you're creepy about it).
Now try to go up to a different person and look angry at them, or yell at them(instead of talking nicely) or be accusatory towards them. The result will be the same, you'll work someone right up to being angry right back at you, possibly more so then you were.
It is proven fact(scientific even) that you act nice to others they'll act nice back(most of the time), heck its the golden rule of many religions and cultures.
As for magick having a color, countless threads on this site have gone into great length to dispute 'color of magick'. Well heres the straight facts, it is no different then dividing school into different classes. You have your history, english, etc. Well with magick you have your different categories of magick, which for simplicity have taken on a color so that it is easier for practitioners to communicate the type of magick they are doing. Much like one would do if they wished to talk about an assignment in english class, just instead of 'english class' it would be a color/type of magick.
Further more, for those about the 'dark arts' heres a little food for thought. The practice of Necromancy(usally falls under black magick/dark arts) is not really dark at all.
Wikipedia: Necromancy (pronounced /nkrm?nsi/; Greek nekromant?a, via Latin necromantia) is a form of magic in which the practitioner seeks to summon the spirit of a deceased person, either as an apparition or ghost, or to raise them bodily, for the purpose of divination.