17 Case study: rgb()

Interface: * Function name and argument names. * alpha has no default but isn’t required. * names not required (imo). * maxColorValue doens’t have most useful default, and not really needed (imo). * Data frame rather than matrix. * Error if function specification is correct * Check for data type, not missingness.

## [1] "#101010"
## [1] "#101010"
## Error: If `r` is data frame, it must have 3 or 4 columns.
## Error: If `r` is a data frame, `b`, `g`, and `a` must not be set.