Comparison Parker Urban Core F309 Muted Black GT vs Parker IM Core F321 Black GT

The colour of the ink originally supplied with the pen, in other words, the colour that the pen writes out of the box, without replacing the refill/cartridge or refilling the ink.

Blue is traditionally used for writing, black is somewhat less common, and red ink is convenient for making corrections. Nevertheless, in addition to these colours, there are others, including rather unusual ones: green, yellow, orange, pink, etc. Keep in mind that other colours can be changed within most modern pens.