Identifying specific hens eggs with food color, experience?

[sarahannecloud9]

I have a mixed flock of hens, only wanting cochin eggs to hatch. I have some I don't think are laying as well. I was told of the food coloring method. Also it will last up to 7 days. I have no clue where to get pipettes? Also looking for others with experience please? Tips?

TIA!!