"O artista veste um chapéu vermelho"
Is 'artista' masculine, even though it ends with an 'a'?
masculine = O artista / feminine = A artista. Some words ended in -a are masculine. (for instance: o dia, o cinema, etc).
It's not common to use "vestir" for hats and many others clothes... the usual is "usar"... O artista usa um chapéu/sapato/cinto... usa uma camisa/calça...
I swear the man's voice does not pronounce the "um" at all in this sentence. :(
He seems to skip a lot of things...
What is an 'artista'? Is it just a painter, or does it include sculptors, or does it include singers? Does the meaning vary with the context?
Yes, artista is anyone involved in Arts.