--help-rgb-colors to

[n1vux]

related to #319 and beyondgrep/website#120 --help-rgb-colors could use $ACK_COLOR_MATCH or --color-match="blink italic underline bold red on_yellow" as the default color value in the Foreground and Background color displays, overriding just the FG color and BG respectively, so that tweaks to a given combination can be evaluated.

(optionally, optional arg --help-rgb-colors=color-filename could cause it to use one of the other 3 color selectors other than Match, to minimize copy-pasta from .ackrc during testing.)