You call that yellowing? That's what people in the hobby call "vintage patina" and it adds character. A book that sat on a shelf for 50 years in a dusty basement deserved to finally see some sunlight, right? The real lesson here is that you got a perfectly readable copy for two bucks and now you're crying about some color change that makes it look authentic. If you wanted museum-grade preservation you should've spent fifty bucks on a sealed copy, not a beat-up Goodwill find. This obsession with keeping everything pristine is why half the collected paperbacks out there look like they're stored in a sterile lab instead of actually being enjoyed.

Buddy of mine did the same thing in Barcelona and it ended up costing him more once he added up the bus fares.

Give it a few more days to dry and you can start calling them "raised panel flooring" instead.

Honestly, you're probably overthinking this and your friend just got lucky. Temperature matters, sure, but water temp isn't some magic switch - I've used tap water straight from the faucet for years and had starters pop off in 5 days flat. Old flour might slow things down a bit, but not by 10 days unless it's literally sawdust. The pineapple juice trick is internet hype, you end up with a sweet starter that acts weird. More likely your kitchen is cold or you're not feeding enough - I'd bet you're skimping on the flour to water ratio. Friend in Denver probably just has a warmer spot for his jar.

Damn that's rough, glad you dodged that bullet.