Post a legible schematic for the t'stat/furnace-input interface; this can be used for a 'brute force' way of figuring out what is going on. This probably shows less than a half dozen wires, and it's the manuf. recommended configuration. Your t'stat manual will show how it's internal switching is matched to its terminal designations.
The colors actually used for each function in your particular case can be sorted out afterwards.
A VOM will soon be necessary. . .