Blood Greaves are +5 skill.
500's only really there for posterity since you need useless crap like Mavi scarf and Mirage charuqs +2 to get it. Max blue magic skill atm is 505. (In salvage only: Mirage Keffiyeh +2, mavi tathlum, mavi scarf, magus jubbah +1, khepri wristbands, antica ring, zaffre cape, ksi sash, mavi tayt +2, mirage charuqs +2
Spoiler: show