How to shade the area between two lines?

[zardoz]

I am logging temperature data from an external sensor and supplying this information to Cacti via a custom SNMP OID. As a result I am obtaining a line which represents the current temperature. However from the RRD file that is generated,I can also find the minimum and maximum temperatures for a particular time period. This results in an extra two lines on my graph representing the minimum and maximum for a day or a week. What I would like to do is to shade the area between these two lines, thereby identifying clearly the range of temperatures for a particular day or week. I have not been able to find any mechanism that allows me to shade between two arbitrary lines, where negative numbers are involved. Does anyone know of any way of doing this such that only the area between the minimum and maximum lines is shaded?

[TheWitness]

For the minimum use a, then for the max use an area fill with the shade color that stacks on top of the line, use a CDEF to subtract max-min and then follow that up with a line at average and a line at max.

The real trick is the STACK and the CDEF.