donut chart- conditional palette

[ALR1995]

Hi everyone,

Hope you're doing great.

i got issue with conditional palette,  i want to show the value of a='rank' and b='100 - rank'. for ex: a =92 and b = 8.

when i use default palette its work each item has color, but when use conditional palette its not work right.

this is conditional palette i use:
b > 0 palette color Silver
a between  10 and 30  palette color Red
a between  30 and 50  palette color Yellow
a > 50 palette color Green

after that is show all palette  Silver !!! why?

please help me

Best Regards,