Hello! I would like to help the best I can and give my two cents.
I first notice that you don't have a particular light source on your piece and I feel like there really isn't any or if there is it seems scattered from place to place I would suggest making a clearer light source.
As well for color theory aaa here I took some of the colors you have and made like what i like to call when testing out colors the "Circle test."
I took and saw that your mouse's fur was a sorta orange when I took it and checked it in my color hue wheel.
Now taking what you said about to color theory in mind I move it towards first a LITTLE towards the red, as red is the warmer color and next to the color wheel from orange. Thus giving us a slightly darker shade of the color. In the process also I adjust the Saturation and Values in order to not make the darker shade not too bright or not too dull!
For the highlight I just moved the hue wheel up from the orangish color to make a sorta yellow and turned down its variation to make it brighter!
And for the lineart or darker shade- I take my shade I made earlier and make a darker than it was say 2x as much-
With my results I was able to create and test out and successfully create a circle!
Also as a helpful tip like me I need references to work with ALOT. So I would highly recommend especially for metal to look up references of how light source works from different angles and such, as well as for metal. I even looked up ref help when making the circle for you uvu; it never hurts to look up for references.
I hope this helps you with color theory at least a little. Or at least helps you in general!
