gradient palette (default=NULL). If NULL, use colorRampPalette(c('gray90','red'), space = "Lab")(1024) if the values are non-negative; otherwise colorRampPalette(c("blue", "grey90", "red"), space = "Lab")(1024) is used
zlim
a two-value vector specifying limits of the values that should correspond to the extremes of the color gradient
gradient.range.quantile
extreme quantiles of values that should be trimmed prior to color mapping (default=0.95)