The male House Sparrow has a black bill in the breeding season and in summer.
In winter the male's bill is lighter in color.
Young males have a yellowish bill.
Females have a yellowish bill all year round.

House Sparrows look similar to Eurasian Tree Sparrows.
If you want to tell them apart, remember that Eurasian Tree Sparrows have a brown cap and House Sparrows have a grey cap.
Male and female House Sparrows look different while male and female Eurasian Tree Sparrows look similar.
In Europe you may find the Eurasian Tree Sparrow in wooded open countryside, while the House Sparrow breeds in the more urban areas.

1st photo: A young male. Istanbul, Turkey, 30 September 2012
2nd photo: Males & females. Gülhane Park, Istanbul, Turkey, 21 September 2012