1. Door sill
2. Most sills are merbau [red colour]
I leave mine natural ['cause that suits] & every 12 months or so [ maybe 5 years or so ] use a paint scraper to remove the grime & give it a swish of sealer oil.
A side door in a previous home was painted & was a pain to keep looking good but I suppose it depends on the overall look.
If it's merbau it doesn't take a stain really well & a painted surface doesn't seem to last with heavy traffic & is a bigger job to bring back.