So, first of all, I'm not sure if orange is actually a colour Parshendi have.
There's also a timeline issue though, in that the parshmen have spent the last two thousand years trapped in slaveform, while Stormlight Archive plays more or less around the same time as Mistborn Era 2, meaning that the last time parshmen weren't in slaveform was about 700 years before the Lord Ruler rose to power. Considering Southern Scadrian culture seems to have formed during the Final Empire (when the planet was much warmer), it is unlikely they were influenced by singers.
Of course, the Parshendi were not trapped in slaveform, but we know they have lost access to the forms for a long time, knowing only dullform (and mateform?), and they seem to have lived only in the far east of Roshar, far away from the only known Perpendicularity (in the Horneater peaks).