Foundation is meant to even out the skin tone, create a perfect smooth complexion and cover slight discolorations and marks on the face. It also provides a blank canvass for more makeup; hence whatever formula of foundation you choose to buy must be the EXACT colour as your complexion and should blend evenly into your face and neck.
When you have foundation that is too light, it gives a ghostly appearance and creates a flash back when photographed and when you have foundation that is too dark, it makes your face look overly tanned and separated from your neck. Foundations aren’t meant to give you a bit of a tan. That’s what bronzers are meant for.
To find the right foundation for your skin tone, you have to test the shade of your desired foundation on your clean face and not on the neck or the back of your hand. It is always advised to visit a makeup studio so as to comfortably test shades and find the right match for your skin tone. If you cannot make it to a studio, it is advised to test on your jaw line before buying and look at your skin in various lighting situations to make sure the shade you choose looks natural.