I saw this post over on Going Concern, and had to share it. It might not be accurate, but it is always fun to combine things that I love, in this case: accounting and Harry Potter.
Using the best research tools at my disposal (e.g. Harry Potter Wiki) I find your initial suggestions to be grossly off the mark. For starters, if one were to simply look at the House Colors Colours of the Four Houses of Hogwarts, you would see Gryffindor is crimson and gold, Slytherin is green and silver, Ravenclaw is blue and silver, Hufflepuff is yellow and black. So from a purely superficial analysis the Houses/Firms would fall in this way: