imho, dont kill me..
1) change the capacitor on tone knob to bigger value, roll down tone knob a bit will darken it faster and more significant then different strings.
2) reduce pot values used in guitar for darker tone
3) up the mids, down the treble and up the bass on amp eq
not sure bout strings that gave warmer tone though. Coz i always find whichever strings, after plugging the guitar into amp, the colouration from pickup, amp eq, cable capacitance if any or thru pedals(with/without) wud have already change the characteristic of the strings ifself