Catmather--
Snap: we're wallet twins.
All of my mulberry pieces have oxblood. I enjoy the color's verve & sophistication.
I don't own a tessie & am unsure about your exact rain concerns. I carry an oxblood natural leather bayswater most days. So, I'll use that purse as example--
Rain: started 2nd day using my bays & continued all week. Everything from drizzle to downpour.
Collonil: mulberry store sprayed leather items with waterstop @ purchase. I applied leather gel before & after rain exposure. Told to spray with waterstop monthly: I prefer using gel.
Results: rain beaded on leather surface & no damage. Left bays indoors during downpour & carried wallet in coat pocket. No creasing or spots on wallet, no color transfer to clothing.
Bonus: no visible marks from inquisitive & wet dog nose, either.
Suggestion: I carry a large, polyester(dries fast) scarf to block unexpected or blowing rain. Just drape over shoulders & purse. Effective.
I think quality pieces age beautifully, though they change & gather imperfections...all part of a unique story. As with people. But, someone focused on product resale may think differently.
I hope this helps. Please enjoy your sassy oxblood items completely, whatever the weather.