a little correction: i wrote that in the third chart the expressions seems to deliver NULL because the cell is gray... but I misread my expression... actually it is gray because it doesn't deliver anything at all.... null would be yellow, not gray.
Looking forward to your tips. :-)
The expression defining the color is an attribute expression, and it will only be calculated if the main expression is calculated. Coloring will not be applied if the first column result is missing or null values. This is a limitation in QlikView. If you can use a Straight Table instead of a Pivot Table you shouldn't experience the problem. If you must use a Pivot Table you can add subtotals on top to as a workaround.
I hope this help.