Hi nyc,
This is expected behaviour if you are modifying the control using the front panel. To change the entire colour range you will need to use property nodes.
I attach an example of how to do this.
Basically you are setting the colour from around 8 - <10 to a colour other than red.
However there is a colour of Red set at point 10 which is next to impossible to change with the paint tool.
Please look at the block diagram of the attached code to see how to modify the control.
Regards
JamesC
NIUK and Ireland