Do you find yourself shopping for concealer and looking at a rainbow of colors, wondering what the difference is if you buy a pink, yellow, or green? I had this problem and never knew what they were used for so I limited myself to purchasing the nude shades which literally were the same as my skin tone for fear that I would start to appear clownish with the rest. Fear not, however, because I'm going to tell you exactly what they're all for so don't be afraid to add them to your arsenal of blemish and imperfection coverage.
In general, concealers hide dark circles, scars, pimples, and really any skin flaw you can think of. It's always important to consider whether or not your concealer is of adequate quality and won't cake on your face, as this will make you flaws stand out even more (not exactly your intended result, is it?). Concealer colors are all about neutralization, since most of our skin's imperfections have a color hue to them. For example, your under-eye circles tend to be blueish in hue, many people have redness on their faces, and pimples can be plenty of colors. As for imperfections that aren't affected by color, such as wrinkles and fine lines, we would stick to using the neutral concealer that just matches your skin tone and foundation.
If you have tattoos and you want to cover them up without spending a pretty penny for your tattoo concealers, use the regular drugstore concealers but consider the color of your tattoo. If you have a blue tattoo, use a concealer that is yellowish and make sure that you have a waterproof formula as well as applying a translucent powder on top to set the product for the longest staying power possible.
Below is a collection of concealers that I am familiar with and that have worked well for me at a reasonable cost.