Most of the spam in the Junk folder has been colored by SpamSieve. However there are a few spam messages with an uncolored background and brown text, so I assume SpamSieve hasn’t seen them. But I don’t know why.
Apple Mail gets its email from two Gmail accounts. Both Gmail accounts have been configured (per Help section 7.6.3) to “Never send it to spam”. Apple Mail has been configured as described in Help 3.1. macOS is v10.15.7.