There's a couple of ways to only color the % value...
One way would be to create two separate views (one for Actual and Proj, and another for the % calculation) and then combine them on a dashbaord. The second view would have it's headers hidden so you don't get repetition of your row headers.
A second way is to add Actual and Proj. as DISCRETE aggregated measures to the row shelf (i.e. a blue pill saying Sum(Actual), or whatever your aggregation is... I cannot see from your screenshot). This way, these two measures are now headers, rather than data. The % then is added to the Text shelf and you can color by itself and it won't affect the headers.
For your red-black-green diverging scheme, you can create a custom color palette by editing the Preferences file in your 'My Tableau Repository' folder. Something like
<color-palette name="My Sequential Palette" type="ordered-diverging" >
might work. More info on custom color palettes here: http://kb.tableausoftware.com/articles/knowledgebase/creating-custom-color-palettes
Custom Colours.twbx.zip 1.1 MB