Colors change in each lot, and sometimes even in each skein. If you want to avoid problems you should combine skeins as you knit. Oh, and try to buy all the skeins you need for your project in one order, the differences between dyeing lots are usually evident.
Every monitor shows colors in a slightly different way, and even though I take a lot of care when I edit the photos, what you see on screen will never be exactly what you see in the real skein. Also, the photos you see on the page are usually not of the same skeins that I am going to send you, although discreet, there are always some variations.
Wash the finished piece carefully in cold water (NOT WARM!!!) and with the same shampoo you use for your hair. You don't need to use vinegar. In the first washes a little dye can be released, so if you are going to use very contrasting colors it is better to knit a small sample and wash it. This is impossible to avoid, so I will repeat it a thousand times if necessary: wash with cold water and shampoo!
If you want to know a little bit more about washing your woolens see this post.