It is difficult to judge the value of local colours when a mid-tone is placed among other mid-tones. Blurring the image by looking through half closed eyes or using black and white photo of the object seems to solve the problem. This way you can establish the outline (shape) of the object (focal point) distinguishing it from the background.
I find that I'd rather like to look for the darkest shapes and then add a mid-tone, then leaving lighter tones as the white of the paper. Keeping it simple as possible helps to not get overwhelmed by the details.