scatter3D in R Colouring Issue with Plane

I am using a scatter3D from the library plot3D and plotting a scatterplot with a plane of predictions:

library(plot3D)   
scatter3D(x1,x2,y, bty = "g",
              pch = 20, cex = 2, ticktype = "detailed",
              surf = list(x = sort(unique(x1_new)), y = sort(unique(x2_new)), z = z.pred ,  
                          facets = NA
                          ))

my y ranges from -1 to 1, however, some predictions in z.pred are lower than -1. Hence you will notice that predictions below -1 are not coloured as they are outside the colour scale. How can I fix that?

Try this:

library(plot3D)   
scatter3D(x1,x2,y, bty = "g",
              pch = 20, cex = 2, ticktype = "detailed",
              surf = list(x = sort(unique(x1_new)), y = sort(unique(x2_new)), z = z.pred ,  
                          facets = NA
                          ),clim=c(min(y,z.pred),max(y,z.pred))