Invisible ink clue in Hexadecimal

69 6E 76 69 73 69 62 6C 65 20 69 6E 6B 20 63 6C 75 65

Character Breakdown

CharHexDecimal
i0x69105
n0x6E110
v0x76118
i0x69105
s0x73115
i0x69105
b0x6298
l0x6C108
e0x65101
0x2032
i0x69105
n0x6E110
k0x6B107
0x2032
c0x6399
l0x6C108
u0x75117
e0x65101