The mice.theme() function sets default choices for
Trellis plots that are built into mice.
mice.theme(transparent = TRUE, alpha.fill = 0.3)A logical indicating whether alpha-transparency is
allowed. The default is TRUE.
A numerical values between 0 and 1 that indicates the default alpha value for fills.
mice.theme() returns a named list that can be used as a theme in the functions in
lattice. By default, the mice.theme() function sets
transparent <- TRUE if the current device .Device supports
semi-transparent colors.