Humidifier Wiring - Aluminum?

I just installed an Aprilaire 700 whole home humidifier and noticed a silver wire was used on some of the parts. Would they really be using aluminum? The 120v transformer they supplied has both leads in this silver wire, is this aluminum or tinned copper? I’m using a wire nut to connect these two leads (hot & n) to copper wire that I can then run to the control board in the furnace, so I don’t want to improperly connect aluminum and copper! Is it safe? Is this really tinned copper? They also have two low voltage wires coming from the humidifier itself that are silver in color, but I assumed since its low voltage connecting these to the 18/2 copper thermostat wire would be ok.
Any info/advice is greatly appreciated.

Photos would help.

More than likely tinned CU…because UL 62 for smaller TFFN and TFN conductors provide a greater option for use on devices with tinning. If it is smaller than 12 AWG and designed after 1972 then it is tinned CU in my opinion. However, yes photos would help.