Color duration-type uda based on value

In my specific setup I defined an uda to estimate the time it will take to complete a task.
```
## Estimate time to complete the task
uda.estimate.label=Estimate
uda.estimate.type=duration
```

I would really like to color my tasks based on that estimate (have quick tasks in green, long tasks in red for instance) with something along those lines:
```
color.uda.estimate.under.10min = green
color.uda.estimate.above.4h = red
```

This would also be nice for the urgency calculation, so all quick tasks are assigned a smaller factor and longer tasks are assigned a bigger one (maybe open an other issue)