Icing question please help party tomorrow

[daysoftheweek]

OK
I'm making a cake from the Australian womens weekly book and I need to make coloured icing so I have a few questions

I have some ready rolled white icing can I use food colouring to change the colour?

I need to make a bright green and black, I have food colouring can I use the two together and if so how? How much food colouring do I use?

thanks

(I think I'll be back later)

If you using ready to roll icing it is much easier to paint the colours on after you iced the cake. You will need to apply the colour a few times to get it very bright.