The answer offered so far (without any upvotes so far) is useful, but incomplete. It is sometimes sufficient to execute install.packages() with dependencies = TRUE, but if the missing package is a dependency of a dependency, then install.package is not "smart" enough to recognize that fact. The ggplot2 package is in the "Depends:" line of the rms package DESCRIPTION file, but colorspace is not. Sometimes the end-user simply needs to read the error message and install the missing dependencies.
In this case, however, it appears that there may have been a version mismatch of packages and R.