sorry for taking so long to reply >3<;;
humm...i'm not really sure what to say in relation to your older colored works, as they're colored in such a different style; it's one that i feel i don't know enough about so i can't really offer any advice on it, though i do think it looks cool
(the ones done in pastels and such, i also like your b&w works)
the more recent one you did in markers is a really good start! unlike my first attempts with prisma markers, the colors are easy on the eyes and blended pretty well, especially on the skin.
what i would suggest is to keep a light source in mind at all times, and shade accordingly. start out with very light shades, of course, and gradually add darker colors/shadows, blending as you go (working in small areas at a time helps, since it's far easier to blend while the ink is still wet.) you may also want to try adding more contrast in certain areas, especially on any parts of the picture that are supposed to look shiny (hair, metal, eyes, etc. should all have darker, crisper shading than more matte things such as cotton clothing.)
i hope this helps O: