Not sure what you're looking for in terms of feedback so I'm just going to start talking...

Looking at your gallery your stuff doesn't look monochrome at all to me. It's great and has a lot of color variety!

If you want to work on being like the reference image, where the light seems to glow out of the objects, then it'll be a bit different from what you have now.

I'd say...your coat would be much brighter and the lines on it would be much lighter. They have a subtle gradient pink > purple at the bottom of the guy's coat/pants there that you could encorporate (but with green > blue or something). Any of their undershirts are black, but you're doing the opposite with a lighter color.

Your skin tone is much darker than what they use and your background is much darker than theirs. I think in their background there's a bit of lingering glow in the air that brightens it a bit. Your hair treatment doesn't seem like it'll match theirs. They have a flat sort of bright color with a few white lines and nice volume defining silhouettes. Also note that the woman has a chunk of hair that is in "shadow" that's a dark orange.

In your gallery you seem to have a good technique for normal hair down fine. Why not try to push yourself by doing their flat, neon style? Right now it feels like you're taking this halfway.

Also they have light hit the very edge of specific skin areas, while you're using volumes of light.

Also you said you were showing your portfolio. What do you want to do with your pixel art? Are you making art to make art? Do you want to advertise? Make games? etc?

I'm at 24 colors so far. Might have to add more shading to the face or reduce the shading in the hair.

Reduced the colors, but I'm not sure about how it looks in the hair now : /

I also think this version is better, but the three purples in the hair all blend together, probably because the darkest orange contrasts too much with them. Try tweaking one or both of those colours? Who knows, maybe it'll make the other areas look better too!

The hair colours look beter!
I don't feel the rimlight is necessary, I think it looked more interesting and more 3D fading into "black". But, it doesn't look bad.
There is a bit much AA in some spots, and not enough in others, I think the problem is that you're AAing too much with the lighter colours, creating overly-smooth light areas that have blocky edges with the dark colours, because you're not using the darker colours for AA enough. Shifting the colours dark-ward starting with the skin-only purple helps. Since that probably made no sense, here's a visual:

I took your existing AA (on the jacket only, I didn't touch the hair) and your existing colours, there are only a couple of small spots where I did any pixel work to eliminate gaps created by the colour shift.
The end result has the same overall shape, but fading more smoothly because it's using more of the dark colours instead of devoting most of the pixels to lighter colours. The bottom-most area of the rimlight could use some #2f044d around it to smooth it more.

Edit: Made the image animate between the two versions.

I don't think the hair needs highlights. If you do add them, keep them very small, perhaps make them sparkles like on the skin.

The jaw shouldn't have that rimlight, unless you really like the look of it. If the jaw has that light, that would mean most of the back should be lit, but it has a rimlight, which means that light is coming from an angle that would not hit the jaw. Similarly, the shirt collar shouldn't have a rimlight running down its entire length because the jacket collar would be blocking it.

I feel that a background is not needed, it would just take away from the character.

Debating if I should put an earring on her or not. Also hope that the BG doesn't distract too much.

wow.
looks very good.
no i wouldnt add an earring.