You have a Photo Black (PK) model; the 309g is a 5-color photo printer. The Photo Black is only used for photo printing, which is why it doesn't cause issues with day-to-day printing.
+
You have a Photo Black (PK) model; the 309g is a 5-color photo printer, HP later got rid of this even on the Photosmart models and reduced them to 4 color CMYK and their photo range took a nosedive :-(. The Photo Black is only used for photo printing, which is why it doesn't cause issues with day-to-day printing.
***COMPLETION ANSWER***
You have a Photo Black (PK) model; the 309g is a 5-color photo printer. The Photo Black is only used for photo printing, which is why it doesn't cause issues with day-to-day printing.