Wow, this is so true! - whether you're talking about a b&w or color image.
Beginners often paint with little attention to value relationships (i.e. degrees of lightness and darkness (not to be confused with color changes). To give life and interest to your piece, to keep the viewers attention - the drawing/paintings should have at least 3, hopefully more, value changes.
In the first image there is very little value change. It's almost monotone. Except for the left side of the piece, most areas are middle gray with a few brighter light touches - barely.
In the second picture, note there are multiple values i.e. lights and darks: the darkest almost black areas (mid-section of stems), the brightest areas (reflection of light on water, next the buds) and then several different mid-gray values (left foreground vs. right foreground vs. right back area vs. water). Finally these value variations were translated into color.
It takes a bit to train the eye to notice value. Try to identify 'value' (lights and darks) when going about your day. If there is an apple sitting on the kitchen table and the morning light comes in through the window squint and look at the 'scene' and pick out:
- the very darkest dark (perhaps in the shadow wear the apple meets the table? or the shadow side of the stem?
- there may also be a dark shadow between the sunlit side of the apple and the back shadowy side....is it darker or lighter than the table shadow.
- Note how the table shadow is darker in some area than another.
- Where is the lightest brightest area?
- What is the 2nd lightest area?
- How does the sunny side of the table look compared to the shadowy side?
I'll share some other images of value in the next few days. Questions?
These little 'cutie' tangerines are sweet to eat and sweet to paint. I worked on value to show how the afternoon light pushed played on the subjects. 
