Mens neklace to go with stainless steel subs – black

I am looking for some advice on the topic of wearing a neklace with my subs.
I am thinking of yellow gold with a crucifix pendant with a diamond in the middle of it.
I do not want a big chain or a big pendant, just a normal size, chain style.
I am.just unsure if mixing the tho diffent coloured metals is the right thing to do.
Could you please your opinion/advice on this?
All replies will be much appreciated.
Thanks