I like everything you've done so far. it reminds me of Boktai backgrounds, I think it's the fuzzy looking ink and the color selection.
I dont see why everything must be overly saturated so as to "jump out" at you, I think the color selection here fits the relaxed fllowing movmenentof the squid.
I'm only concerned about how you will aproach the tentacles.
make sure you dont use every shade on every tentacle, try to create some depth by being selective on which tentacle is highlighted and which isnt, strange as it may sound that creates better depth than using everything everywhere.