Prevention of a possible blooper

After reading the wonderful hair colour article by William, I`m wondering where I can find online (most convienient for me) a chart of hair colour levels. This way I can see if I can actually do to my hair what I am fantasizing in my mind (You know, turning Elthel Murman into Sophia Loren). Also, how accurate are color strand tests? I once had an interesting incident when colouring from blonde to red a blonde-red striped fiasco that was thankfully fixed by a second bottle of Feria. Needless to say, I don`t know if I can so easily fix going from a medium brown into a *lighter* color.
Thank you in advance for your advice!