I am seeing a similar issue. I am using Mathematica 12.2.0.0 on Mac OS10.15.7. Is this still a bug? Is there a solution besides mapping the data as shared by Marc (above)? P.S. This is my first post so I'm not sure how this works...

bl = BarLegend[{palette, {0, 4}}, LabelStyle -> 10];

getColor[val2_] := ColorData["TemperatureMap", val2/4];

{getColor[.1], getColor[1], getColor[1.5], getColor[2], getColor[2.5],
  getColor[3], getColor[3.5], getColor[4]}

gPlot = <|Entity[
    "AdministrativeDivision", {"FairfieldCounty", "Connecticut", 
     "UnitedStates"}] -> Log10[10000.], 
  Entity["AdministrativeDivision", {"HartfordCounty", "Connecticut", 
     "UnitedStates"}] -> Log10[5000.], 
  Entity["AdministrativeDivision", {"LitchfieldCounty", "Connecticut",
      "UnitedStates"}] -> Log10[1000.], 
  Entity["AdministrativeDivision", {"MiddlesexCounty", "Connecticut", 
     "UnitedStates"}] -> Log10[500.], 
  Entity["AdministrativeDivision", {"NewHavenCounty", "Connecticut", 
     "UnitedStates"}] -> Log10[100.], 
  Entity["AdministrativeDivision", {"NewLondonCounty", "Connecticut", 
     "UnitedStates"}] -> Log10[50.], 
  Entity["AdministrativeDivision", {"TollandCounty", "Connecticut", 
     "UnitedStates"}] -> Log10[10.], 
  Entity["AdministrativeDivision", {"WindhamCounty", "Connecticut", 
     "UnitedStates"}] -> Log10[5.]|>

GeoRegionValuePlot[gPlot,
 ImageSize -> 400,
 PlotRange -> {0, 4},
 ColorFunction -> (getColor[#] &),
 ColorFunctionScaling -> False,
 PlotLegends -> bl,
 PlotStyle -> Directive[Opacity[.6]]]

Thank you very much.

Did [url=http://www.testlink.com/]test link[/url] you try doing this in an earlier version of the software, Marc?

Thanks for sharing the workaround, Marc. I used it to ensure the correct color values in the RegionValuePlot in Mathematica version 12.

Today, I ran into an issue with a custom ColorFunction in RegionValuePlot, which showed colors for US Sates inconsistent with their corresponding values.

Cheers,

Dave

I'm using Version 11.3 on Windows 8.1. I've checked with Version 11.2, and I get the same.

I'm using Version 10.1 running Windows 7. Executing code in your In[161], Paris and London were red and Berlin was green.