Choosing foundations can sometimes be difficult. You can make your way to make-up counters and ask professionals to help and even sometimes they fail you. I think the main reason it is so difficult is because most department and drug stores have artificial lighting which makes choosing your correct colour a bit difficult.
I also think the techniques we tend to use to check if a foundation matches our skintone is wrong as well. Most women check on the backs of the hands or on their wrists. This is the first mistake to make as our hands are typically a different colour than our faces no mater how pale or dark our skin colour is.
1. Start choosing a foundation and testing it along your chin and neck. If the the colour blends invisibly from your chin to your neck then you have the correct colour. If you can see the colour from chin to neck then it is either too light or too dark.
2. Test the foundation as above, then go outside into natural light, whether it is sunny or overcast. If you can't see the transition from chin to neck then the colour is correct.
I know it seems like a bit of a hassle, but I would much rather do that then go out with an orange or incredibly pale face!
3. Don't trust make-up counter staff. Though they are probably trained artists and do know what they are talking about, again they are looking at you in artificial light and may misguide you in the colours you require.
4. Take into consideration seasonal and fake tan changes. I recommend having two colours of foundations. One colour should be your skin tone when you are at your lightest and one for when you are at your darkest. Transitioning from summer to winter can mean your skin lightens a bit but not as much as being deep into the winter months. Learn to mix you colours. Take your darkest colour and add a bit if your lighter foundation to it to bring you through autumn.