Replacing wall switch with wireless relay receiver
Sounds like a commonplace switch arrangement to me, the kind where the power comes to the switch and then to the lamp.   This is the simplest type (in tems of understanding it) where hot+neutral come first to the switch, hot is switched, then switched-hot+neutral proceed to the lamp.  

Yellow is rarely seen in residential wiring.  I think they are actually white, but faded.  One is neutral from the panel and the other is neutral to the lamp. 

If I'm right, you're in luck: you have the exact wires the smart switch requires. (Which is often not the case.)