Darker Cornish paintings maybe more popular if very quietly forgotten (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

SW(abbrev. for “South-West”, used to indicate that part of England in which Cornwall is) + ART(one form of which are paintings) + “hipper”(more hip/more popular/trendy) minus ( if … forgotten ) “pp”(abbrev. for “pianissimo”, a musical instruction to play very quietly).