C wire is orange. Y wire is black?

[darrinrigo]

See picture below. This is a furnace only (no AC) and I'm installing a Nest Learning (3rd Gen).

I'm just not sure what to do - I thought Y was only for AC units (and should be yellow?) and I read that C wires should be blue?

[laurentbourg]

The color standards are not always respected, so ignore the color of the wires and only focus on where they are connected on your thermostat. I am not clear why Y is connected if it’s a heat only furnace, I would put electric tape on it and connect all the other wires per below and try the setup. 
- red to Rh
-orange to C
- white to W1
- green to G

[laurentbourg]

Also suggest that before installing the Nest per previous email, disconnect the Y on your old thermostat and ensure that everything works well.