What used to be euphemistically called "Jewelers Bronze" - red brass by another name, 'Nu-Gold" by yet another - is the standard for Western style soldered on overlays.
Take a look at Rio Grande red brass sheet and test a sample... it does tarnish eventually, but still looks fairly good even then.
However, 10K gold filled sheet is not all that expensive and definitely keeps its color.
We used to have it made for us in various colors and karats with a solder flush on the backside.
This does get expensive, because although you can roughly specify how many ounces you want - there is a minimum run.
And if the the mill run is over by a few ounces - you pay the extra. Luck of the draw, so to speak.
Brian
You do NOT want "yellow" brass... for most overlay purposes. Or even for engraving, if you can avoid it.
brian: i'm shocked you would do such a thing. whilst a sailor aboard a us navy ship, when officers would come aboard, straight from annapolis,
they would be sent everywhere by the captain. they were to get him a can of relative bearing grease ! seems they always came up empty handed.