It's when your blind date shows up wearing Oakleys, but looks more like Lassie than Cameron Diaz.
Beyond that, Krell1 is correct. The RCA shaded dogs are the LP pressings where the RCA dog on the label is not white, but illustrated with grades of shading that outline his body parts.
Typically these series of pressings are numbered as LSC **** ( 4 digit numeral) and the designation "Living Stereo."
The Classical (LSC "Living Stereo Classical"), are the valuable ones. There are shaded dogs in the LSP ( LIving Stereo Popular) pressings, but few have any value.