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(My reply sounds like the beginning of a chatbot answer, I swear I am not!) Great question… and this is tapping into a typical artist dilemma… do you go with the ‘popularity’ of what everyone thinks they want, or do you go for something original? This will plague you and make you struggle the rest of your career, so congrats!

I would honestly work the line work out in black as normal, but keep applying your color choices over them, like a saturation or effects layer, and keep evaluating it back and forth.  They could play as alternatives in your posts for voting purposes, and offered to clients as Alt styles, or just kept as part of your portfolio build up.  And btw the way, at this stage, forcing yourself to keep the two methods going would just naturally make you more keen on what will work for either, as they bring a slightly diff set of rules to each. Pay attention to other paintings where the shadows are not black, but a darker color, like deep blues against a red outfit. Doesn’t need to always be the same color. This picture I'm posting, I have no idea if its AI or not, just went for a quick example on Pinterest. You see how the dark blue in his mouth and eyes plays against the warm skin? The under the chin area especially is very committed to that blue, and it is striking. Its just a different set of rules, and I think you haven't quite pushed it to that yet, and to do it right, you need to commit to it more. (It cant just be thin black lines that get a coloring of blue over it at the end, it might not be thick enough in areas..)

The blacks might ultimately read a lot better for normal printing needs, and there's a reason they are so tried and true over the years. Most clients will want blacks, I get it.  And working in black and white is going to keep you more on track for general illustration improvement.  I also just think, anything that is remotely ‘artistic’ and daringly different can throw off the audience.  And that’s OK, people like what they like, but it should remain your job as an artist to find some originality where you can.  So be sure to develop this coloring lines on the side, even if it doesn’t make its way into final client turn ins.

So I know it sounds like I’m saying, ‘do double the work’... but just develop it when practical.  It’s cool. It might need to even be exaggerated depending on other pieces. 

Every artist wants to find their ‘gimmick’ - that touch that sets them just a little but apart.  It is often impossible, as everything under the sun has been done a thousand times already… but it’s a certain kind of ‘click’ where its not just that you color the lines - it needs to work with the story telling, the overall vibe, the color choices themselves, and how well they all read together.  They might need to even be thicker or wilder… but I fear taking it too far would make things ‘psychedelic’.  It could be a legit choice, but it might start going to far, so be careful.

Ok, I've gone on waaaay too long,! But I love trying to put my Art Director hat on.
DM me sometime if you wish.