dog friendly food colouring - any ideas?

[LinzHenz]

Hello!
I've started making my own dog biscuits. I wanted to make some personalised ones for presents and want to colour some dough to write the dogs name with, on top of the main biscuit. Is it safe to use normal food colouring? Or is there something i should watch out for?
The biscuits are v popular even with the fussy eaters so hoping to make some as xmas pressies :-)

[Anita D]

you can push blueberries (purple) and strawberries / raspberries (pink) through a sieve and use the juice that comes out to dye your dough/icing.  You can also use blueberry carton juice from the supermarket.