In your first example, the data doesn't seem to contain both positive and negative values.
The way you would get the desired result (if I understand your requirement correctly) would be to manually set the center point to zero, (although if your data had positive and negatives this should happen automatically)
If you want it to be a solid red for all negatives then set your start value to something like -1 with "Use full color Range"
(I used red white green diverging)
All negatives will be solid red and all positives will be shades of green based off of the measure.
The second request just requires a color calc.
I don't know what the relationship of your two data sources is but the calc would look something like:
IF [ROI Calc] > [Sheet1 (Sample Forecast File_CPA.xls)].[Forecast ROI Calc] THEN -1 ELSE [Some Measure] end
Put that calc on your color shelf and configure the color settings similar to the above.
( I put "Some Measure" in the above calc because I'm not sure what you want shown if actual ROI is > than forecasted)