who designed it?
Julien van der Wal .
Flag of Saint Vincent and the Grenadines
 Consequently, Julien van der Wal – a graphic artist from Switzerland who also designed the flag of the Canton of Geneva and pictograms for the Olympic Games – was tasked with modifying the flag. 
what is the flag of saint vincent and the grenadines? A Canadian pale triband.
wiki:1898804
Flag of Saint Vincent and the Grenadines [SEP] History
However, this design soon proved to be convoluted and costly to manufacture, with the breadfruit leaf hard to recognise from afar. After the New Democratic Party emerged victorious in the 1984 elections, new prime minister James Fitz-Allen Mitchell sought to have the flag redesigned. A nationwide contest was held, but it resulted in an impasse after no entry was deemed suitable. Consequently, Julien van der Wal – a graphic artist from Switzerland who also designed the flag of the Canton of Geneva and pictograms for the Olympic Games – was tasked with modifying the flag. He was instructed to "modernize the original flag, keeping the same colours and respecting the symbolism".