spplot contour font size and color adjustment

Dear list,

I am struggling with the spplot function, in detail, a) labeling some
contours superimposed on a grid. How can I control the contour's font
size? b) How can I set values above 0.6 transparent?

I played around using panel utility functions for spplot but got no
appropriate solution.

# example
library(sp)
data(meuse.grid)
gridded(meuse.grid) = ~x+y
densplot <- spplot(meuse.grid, c("dist"),
   col.regions=rev(gray.colors(20)), contour=T, labels=T, pretty=T,
   panel = function(...) {
     panel.gridplot(...)
     #sp.lines(...)
     })
print(densplot)

I appreciate every hint!

Best regards
Marco

Marco Helbich
Chair of GIScience
Department of Geography, University of Heidelberg
marco.helbich at geog.uni-heidelberg.de
Berliner Stra?e 48, D-69120 Heidelberg, Germany