djmurphy420/ggplot2-transition-guide — comment on commit ae050eb3133ce559adc1488edb96231fb2b08081
File: ggplot2-0.9.0-BW.Rnw line 1353
By yihui:

One logical variable is enough to control two types of chunks: when you want BW version, you turn it on `bw_version=TRUE`; when you want colored, use `bw_version=FALSE`. Another variable like `col_version` is redundant since it is always true that `col_version == !bw_version`.