Improving perspective... Well now that's mentioned, the sprite looks awfully flat. I changed the perspective to be facing more to the side.
I added shading with much stronger shadows to try to give it more depth, via using value contrasts. I think it's interesting you changed the hue and not the value to shade... changing the hue is important and it kind of works in this case since some hues appear at different values, but we can push our value contrasts much farther. IMO dark shadows are also a must-have if you want to make dark outlines work with shading. I've seen plenty of art with weaker shadows that made dark outlines look out of place
You can also 'overlap' things and place things in front or behind things to give an illusion of depth. Kinda what I did with the tentacles, which I even applied a wee bit on the bottom tentacles.
EDIT: I also changed the colors (and the presentation) to have a red-cyan color scheme. They contrast each other very nicely.
Plenty of things that can be polished up on my own sprite edit. I'm feeling clueless with highlights but thankfully you mostly want shadows to convey form anyways. The far upper tentacle ends up looking flat since I'm being too cautious about my rendering craftsmanship
But most of this comes from getting your brain to switch to '3-D mode' and not just seeing your flat canvas as a 2D plane. There's this nifty book I know out there called 'Drawing on the Right Side of the Brain' which talks about the psychological stuff behind what makes some people naturally 'good' at drawing while some people struggle a lot, but once you understand that difference drawing becomes much easier. If you haven't heard of that book before, I think it's a fun read anyways.