It's been raining for the past two days, and amidst the grey I saw a flash of orange! I found what appears to be slime mold growing on a piece of dead blackberry vine caught in the fence.
Let me know what you think, or if you think it could be something else!
Edit
Update: I believe it is actually Coral Spot, a type of fungus! It normally affects trees, but I cannot find any instances of it affecting a blackberry vine. I will be keeping an eye out for more information!