If you are going to purchase your foundation on your own the best way to test it would be on your face and not your hand or your forearm. Your hands spend a lot of time in the sun, in chemicals and often without hand cream so to test any colours on there will be a mistake. Instead go to the make-up counter and apply a small amount onto your chin area and blend it into your neck. The foundation should give you coverage without looking too far from your skin naturally. The colour should compliment not stand out and it should do so with a light finish and not heavy application. When you purchase a powder it should be in a similar tone to your foundation, but it shouldn’t be a powder providing coverage if you are planning on using it at the same time as your foundation. The consistancy should be light and airy and not thick and sticky so go for something light-weight so that it doesn’t end up making your skin look either lighter or darker.