I want to visualize a value that indicates the amount of deviation a certain resource's value is from its default value. In this specific case, a higher deviation is bad and a low one is good. So in short, I want to visualize the fact that the lower the deviation, the better. I want to visualize the actual value itself as well.
A number with a value with a color scale going from green to red sounds like a solution, but I cannot tie a scale to absolute specific values. In other words, 0 (zero) might be green, but pure red is not necessarily 100. Next to that, I'd like to stay away from using colors for text that should be read easily anyway. Yellow text (somewhere between green and red in the scale) on top of a white background is terrible in regards to legibility.
How should I tackle this? Are there examples that try to do similar things?