Color theory becomes really important for artists who want to delve into use of colors (people who do advertising and design), BUT, like everyone says manga's don't really use colors inside your actual panels (unless its a special addition, cover, or inlays usually the cost of time would make that specific manga pretty expensive). Generally you would use tones/screentones/overlays and you can definitely take on your own personal style (sharper lines, contrasting weight difference when it comes to more dynamic pictures). Also, if you DID want to add color to your work, you could just choose one highlighting color - no shades or highlights. For example if you were writing a horror story you could throw in red as a bold pop to important scenes.
Most of the time, if you are actually working in the comic industry you would take on one role within the whole comic making process. For example, if you work for DC comics, you could take on the role of just doing the inking of an image. Then it would get sent to a colorist and then it would get sent to a typographer to do lettering. (This is for big ongoing comic stories). However, if you did your own comic online like mentioned @Ryan Dave Jimenez , your work really could be overlooked because of the lack of color....even if the story is well made. I personally think that solely depends on the format the comic takes as this isn't always the case - strip comics reading from top to bottom in a line... unless the work is dynamic, would be not as interesting as colored work.
Anyways, please don't give up dreams to become a comic artist. Being able to do color would be an asset but not a requirement. As mentioned, you could always hire someone to color for you, OR find a friend you could collaborate with.