bug fix when color data is updated
bug fix when color data is updated

rmenegaux/bqplot,ChakriCherukuri/bqplot,dmadeka/bqplot,ChakriCherukuri/bqplot,ssunkara1/bqplot,ssunkara1/bqplot,SylvainCorlay/bqplot,SylvainCorlay/bqplot,SylvainCorlay/bqplot,ChakriCherukuri/bqplot,bloomberg/bqplot,rmenegaux/bqplot,bloomberg/bqplot,dmadeka/bqplot,bloomberg/bqplot