If I understand your request, you want C1 to be blank if it is empty or if it
equals A1. If it is greater than A1, change it to one color. If it is less
than A1, change it to another color.
In the Conditional Formatting dialog, for Condition 1 Formula Is enter
=AND(LEN(C1)>0,C1>A1)
Use the Format button to specify the color C1 should be if it is greater
than A1.
Click the Add>> button to add another condition.
In the Conditional Formatting dialog, for Condition 2 Formula Is enter
=AND(LEN(C1)>0,C1<A1)
Use the Format button to specify the color C1 should be if it is less than A1.
Hope this helps,
Hutch