The short answer is “you can’t”. Colors are helpful for us humans to understand the results but computers represent them as 3 integers from 0 to 255, which is not really translate-able to a floating point number. Or at least not reliably so.
This is why all Ladybug Tools components will give you the actual list of numbers whenever there’s a colored mesh output from a component. And, as @minggangyin said, you can use these numbers in your visualization if you want.