I’m seeing large blocks of uncolored messages in iCloud Spam file. I have no rules that send to Spam, and junk mail filtering is turned off in Mail Setup. The messages do appear to be spam, but I don’t think SpamSieve is processing them. So who is?
iCloud has a server junk filter that is always active. The messages that it catches will have brown text on a white background, whereas the SpamSieve ones will have brown text on a colored background.
It is also possible to have messages with a white background in the Junk mailbox if they were moved by another copy of SpamSieve running on a different Mac. This is because Mail doesn’t sync the background colors.