yellow flames indicate less than optimal mix at the burner. is this a pilot style or ignition style burner? older pilot light style stove at the church would get yellow flames on pilot lights if deposits build up around the orifice.
step 1...double and triple check the fittings you recently put in with soapy water, look for bubbles. it's not a bad idea to check other fittings on the line even if you didn't recently mess with them.
step 2...check for deposits, dirt or clogs at the burners fouling the holes. maybe messing with the lines jarred some gunk loose.
step 3...if the above two check out and you still have a yellowish flame then tweak the adjustment screw on the burner to get back to a nice blue flame.