Honeywell 50 va transformer wire-code

dk_6

To all,

I have a honeywell transformer AT150D1019 for the gas steam heat, I would like to ask the color code of the 4 wires represent? in the primary there are white and black, and I assume the black is for the hot,in the secondary, there are blue and yellow, so which one is hot in the secondary then? or just don't care? thank you very much in advance.