GRAYSCALE PAINTING | this tribe thing

sometimes a client tells me that i should charge them cheaper because they want grayscale illustration, not colour. well, i dont agree, because i actually find painting in monotone more difficult than painting in full colour. when doing colours, it's kinda like they help you make the thing look good. but with a monotone pallette, i find myself doing more work to make a scene look good, like this one i'm working on for a book.

i'm i doing something wrong? coz some artists i know find monotone work easier.

click for a closer look: