Your first question about individually coloring each metric is dead-on. I have a blog post about how to do it at http://breaking-bi.blogspot.com/2013/02/formatting-individual-columns-in.html. As to your second question, you can only apply one value to be colored on for each mark type. However, the complexity of that value can be high enough to emulate having multiple coloring schemes. A simple example:
Columns has percentages and flat values (which are always) greater than 100
You want negative percentages to be orange,
Positive Percentages to be blue,
Flat Values to be black
Create the following calculation
IF [Value] < 0 THEN "Orange"
ELSEIF [Value] > 100 THEN "Black"
Let me know if this helps,
Thank you so much for your information. This is really very helpful to me.