Answer:
monochromatic
Explanation:
I took art classes for 3 years and I always knew that a monochromatic "drawing" or "picture" was something that contained one "base color".
ex. blue, it could be royal blue, light blue, navy blue, as long as they were in the same base, it's monochromatic.
mono = "only"
chromatic = (technically) "color"
monochromatic = "only (one) color"
also, don't confuse "shade" with "color". ex. color is blue, but the shade is light blue. you can have many different shades in a monochromatic "picture", but you can only have one color. :)