I doubt you can do this with true Conditional Formatting if that's what your title is suggesting. My guess is that you would need a shape that using a gradient fill and change its length based on some factor. In your case this may be the max value you could expect to have for the bar. However, if you create long shapes and compress them when values are low, there won't be much gradient to see. Personally I think that the eye candy effect you're after would not be worth the effort it takes. Perhaps someone will have a better idea that shapes with gradient fills.