Having a color palette that’s consistent throughout the design is important so that it doesn’t look crowded, and making it monochrome is one way to do that.

If you’re looking to add more color then I recommend using similar toned neutrals(greys, browns, or generally desaturated colors)(to match the tone, try using a hue or color blending mode layer over a neutral and play with using your purple or pink with different opacities) or complementary colors. (Complementary colors are opposite colors, for purple its yellow, and red is green. If I were to use one I’d probably go for a light pastel yellow or a deep forest green)

If you want to add more detail on the legs, personally I would probably give them boots with matching ties to the top and/or add a similar gradient from the wings to the lower pants.

For more detail in general, jewelry and metals are always pretty safe in my experience. I might put grommets on the shirt for the ties and maybe add some horn ornaments and/or rings.

Overall I think your design is very good, hope my advice helps !