What would the colour of the killing curse if Snape shot it at Harry ?

I was just wondering because I just watched the Half-blood prince on DVD today and when Snape shot the killing curse at Dumbledore the colour of the curse was blue not green (I read the book too and I know it wasn't even blue it was green in the book but forget the book for a second) so I was thiking that maybe it was blue because Snape never wanted to kill Dumbledore right...so blue was probably a sign of sadness? Depression? you know because the colour was blue...So I was thinking what if Snape was the one who should kill Harry not Voldemort what do you think the colour of the curse would be if Snape tried to kill Harry (out of orders from Dumbledore)?
Any colour you like it doesn't have to be blue because of depression or green because of joy it could be for example red because of anger (I know its the colour of the Expelliarmus spell but forget that tiny detail)So in your opinion what would the colour of the killing curse would be if Snape shot Harry ?
P.S(If you dont get it I meant what would the colour of the killing curse be depending Snape's feelling about killing Harry)