>>>May be it's a problem in VFP8 version I'm using, but I can not change the number by typing it in the text portion. It only allows me to type one digit instead of the number.
>>
>>
>>I have no problems with VFP8 also, of course this code will change color at every single keystroke.
>
>BTW, does Keyboard input works correctly for you? I can enter any number outside the range and get an error, of course. What's the purpose of KeyboardLowVal/HighVal then?

IAC is fired before the check of the High and Low values, so if you want to be correct in IAC you must add something like:

IF BETWEEN(this.Value, 0, 255)
   .....
ENDIF

But I was too lazy to do that :-)