changing cell color based on value of another cell?

conditional formatting should do this for you

it would be better with a sample spreadsheet - let me see meanwhile

fill what cells

for 2007, 2010 , 2013 , 2016 , 2019 or 365 Subscription excel version
Conditional Formatting

Highlight applicable range >>
select the range you want to fill- lets say column C c2:c100 - Change, reduce or extend the rows to meet your data range of rows

Home Tab >> Styles >> Conditional Formatting
New Rule >> Use a formula to determine which cells to format
Edit the Rule Description: Format values where this formula is true:
=AND($D2<0.9,$D2<>"")

Format [Number, Font, Border, Fill]
choose the format you would like to apply when the condition is true
OK >> OK

New rule and use
=$D2>1.1

new rule
=$D2>=0.9

put in that order
use stop if true and then should be OK, otherwise the >0.9 will overwrite the >1.1

but what colour if it equals the values
0.9 , 1.1

you need to explain a little more
is it columns I and M you want to colour
you said not clear now on what column the % you want to test is in
C is a description now and not

column (c) divides a/b and reports as a "percentage"

and

based on that value, in another column (d),

D = routing and not a %

so i think a fuller explanation is required
BUT
the formulas still apply - select the range you want to colour and use the formulas as i posted - just change the column from D to whatever % column you are testing

ok,
i applied 3 rules - and selected F5 to F40 - you can extend the rows to 100 , 1000 whatever , as i test each cell for a number
but as we dont want to highlight the titles/text or blank cells i have used
RED
=AND(ISNUMBER($F5),$F5<>"",$F5<0.9)

it checks to see if F5 and then each cell to F40 to see if it is a number -
then if F5 to F40 cell is not blank
and then to colour RED if the cell is below 90%

YELLOW
=AND(ISNUMBER($F5),$F5<>"",$F5>1.1)

GREEN
=AND(ISNUMBER($F5),$F5<>"",$F5>=0.9)

and put in that order and used stop if true
so if its over 110% it will be yellow and stop - otherwise it would be green as i just say >-90% so anythign over 110% would also be green if tht was allowed to test - but the order of yellow 1st and stop if true prevent that
but we could add another and value for green
=AND(ISNUMBER($F5),$F5<>"",$F5>=0.9, $F5<=1.1)

AS i have selected the range starting at row 5 - then the formula also has to start at row 5

you are welcome,

i hate asking for things like this ...

no problem thats what the forums are for , any questions.....

but get cast into the role often

I was a electronic/computer engineer and looked after the companies stats field service system and then i got asked about some of the KPI's and reports it produced, that was in 1982, and then had to use lotus 123 for those reports and started helping out and that sort of defined my career into KPI. performance , MI , change management , Business planning , luckily the company (DEC) did invest in training and obtaining professional qualifications in those days, including SQL, Excel, Access and various change/facilitation and management training etc etc