Hello! :D
I know this is VERY late to post any answer but it kinda a sad forum post without any replies ^_^

I think "Yellow" by Coldplay would do with any shipping with Yellow in ;)
This song is just a kinda cute and calm song i find to fit Yellow perfectly and then i could imagine
her partner singing it to her

You might have seen it already but i once stumbled on a amazing shipping video
I had just some random pokéspe characters in it but it was using the song
"Fool like me" by Cobra Starship and i find it to fit any shipping with Gold perfectly! :D

I have also just realized that "Uncover" by Zara Larrson Fits amazingly well with Gold X Silver
(Is it wrong that i feel kinda trolling for saying that? XD)

A last one would be "Let her go" by Passenger for Sapphire X Ruby. I think it fits really well when
Sapphire confessed her love to Ruby but Ruby denied his love for Sapphire (i have not actually read
that far so i might be wrong ^_^)

Here ya' go! I was really bored and although i doubt that you are even ever online anymore
then... Here ya' go! :D