filled.contour and NA's

I'm trying to do a filled.contour plot where some points are labelled as
NA. How do I could plot this kind of graphics, so NA points are coloured
black,  keeping the levels of remaining points. NA's values represent
land points (meaningless), and what I want to plot is the levels of a
variable over the sea.

You can also do this using ggplot, although you don't have quite as
much control over the appearance of the contours (you do get more
control over other things)

install.packages("ggplot", dep=T)
library(ggplot)

# Set up appropriate data structure
dimnames(ene) <- list(y, x)
names(dimnames(ene)) <- c("y", "x")
enem <- melt(ene)

p <- ggplot(na.omit(enem), aes=list(x=x, y=y, z=value, fill=value))
p <- ggtile(p)
p <- ggcontour(p)
scfillgradient(p)
scfillgradient(p, low="white", high="blue")

Regards,

Hadley