As a prerequisite you're first going to create your two CDEFs, one for the green area and one for the yellow area. The threshold is set at 50, but you can change this to fit your needs. Let's have a look at the two CDEFs you're going to create shortly:

CDEF:isGreen=intspeed,0,44,LIMIT
CDEF:isYellow=intspeed,45,50,LIMIT

Cacti does not use named variables like intspeed but defines them according to the alphabet from a to z, so your definition from a Cacti view actually looks like:

CDEF:cdefa=a,0,44,LIMIT
CDEF:cdefb=a,45,50,LIMIT

isGreen and isYellow have also been changed. Don't worry, Cacti takes care of this automatically. Just remember that your green area will go from 0 to 44, the yellow area will show up once the number of process are between 45 and 50 and the red area will show above 50.