This is a great explanation for the uninitiated. Kudos. You can get the green stuff in any color, of course. Hence red or blue circuit boards. There is lore

This is a great explanation for the uninitiated. Kudos. You can get the green stuff in any color, of course. Hence red or blue circuit boards. There is lore about why green but whether it was chosen deliberately, copper traces appear darker through green than other colors because they're reddish. So one might prefer green for development. The natural color of the most common fiberglass used in circuit boards is a straw color - you will see this from time to time, either on very low cost boards or where solder mask has been deliberately left off. Vias were literally rivets in the very early days of PCB fabrication. Someone might still be selling a kit of that kind of thing for people who etch boards themselves. I'm not going to look, but they were still around 20 years ago, they were obsolete then, and things hang around in this industry for a long time after they're obsolete. Actual through-rivets have very poor mechanical performance and crack easily. Vias and through-holes for parts leads are typically plated now. You can only get plated through holes from the quick-turn suppliers hobbyists use, and that's a good thing.