sexing rhode island reds /black rocks

Hi i,ve got 3 chicks which are a rhode island /black rock cross one is obviously black the other two rhodies they are about 3 weeks old .They all have a yellow comb and all really look similar apart from the colour .Are they easy to sex at this age
Ps i would love to post a photo but dont know how could someone talk me thru the procedure? cheers slurp

You can't sex them by down colour. Only the original cross does that AFAIK

all the combs are the same cant see any differences in any of the chicks