How can define separate thresholds for some items

According to attach pic I have different items for example
DB-[SYSTEM] is showing 25G
DB2[SYSAUX] is showing 22G
but as you can see threshold for all of them is set for 30 "that means each of them is less than 30 color changes to red , But want to define specific threshold for each of them for example if
DB-[SYSTEM] is less than 30G color changes to red and if DB2[SYSAUX] is less than 23G color changes to green . How can do it ?

what if you tried value mapping ranges instead of thresholds? Or do you want different coloring not only by value but also metric name?