The colour listed as 'transparent' is specific to the $Color attribute of Map adornments alone; note the lowercase initial letter, transparent, as the spelling is case-sensitive.
Setting a value of transparent makes the body and border of the adornment colourless (i.e. transparent). If the $NameColor attribute ('Text color' on dialog) is still set to automatic then it will use the container's background colour as that against which the appropriate black/white colour will be used for the adornment title (if any).