The package lets you shade or colour the cells in the alignment
environments such as \halign and LaTeX's tabular and array
environments. The colortbl package is to be preferred today
with LaTeX (it assures compatibility with the longtable
package, which is no longer true with colortab); another modern
option is the table-colouring option of the xcolor. However,
colortab remains an adequate solution for use with Plain TeX.
