The color listed as 'automatic' is used by the $NameColor and $BorderColor attributes; note the lowercase initial letter - automatic - as the spelling is case-sensitive.
In the NameColor context Tinderbox toggles the text color from black to White and vice-versa depending on the color value in 'Color'. In the context of $BorderColor the bevel colours used are lighter and darker gradations of the value specified for 'Color' so as to not contrast unduly with the main 'face' color of the note (especially in Map view).
If automatic is displayed as one of a note's key attributes, the colour chip for 'automatic' always shows as a dark red (#6F0000) regardless of the colour actually used, e.g. $NameColor may show as white in Map view but as dark red in the note's colour chip. If Color-type attributes that don't support the 'automatic' token are set to the value 'automatic' the resulting colour actually used is #6F0000. In some later versions, this 'mis-set' color equates to a green, #00D001.
This value cannot be customised by the user, unlike other named colours.