Use Microsoft.NETFramework.ReferenceAssemblies

ThemeEditor.sln

@@ -39,6 +39,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "props", "props", "{A88815F2
 		build\Linker.props = build\Linker.props
 		build\Newtonsoft.Json.props = build\Newtonsoft.Json.props
 		build\ReactiveUI.props = build\ReactiveUI.props
+		build\ReferenceAssemblies.props = build\ReferenceAssemblies.props
 		build\Rx.props = build\Rx.props
 		build\XUnit.props = build\XUnit.props
 	EndProjectSection

build/ReferenceAssemblies.props

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.0-preview.1" />
+  </ItemGroup>
+</Project>

src/ThemeEditor.Controls.ColorPicker/ThemeEditor.Controls.ColorPicker.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFramework>netstandard2.0;net461</TargetFramework>
     <OutputType>Library</OutputType>
     <EnableDefaultCompileItems>False</EnableDefaultCompileItems>
     <LangVersion>latest</LangVersion>
@@ -13,6 +13,7 @@
   </PropertyGroup>
 
   <Import Project="..\..\build\Base.props" />
+  <Import Project="..\..\build\ReferenceAssemblies.props" />
   <Import Project="..\..\build\Rx.props" />
   <Import Project="..\..\build\Avalonia.props" />
 

src/ThemeEditor/ThemeEditor.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <TargetFrameworks>netcoreapp3.0;net461</TargetFrameworks>
     <OutputType>WinExe</OutputType>
     <EnableDefaultCompileItems>False</EnableDefaultCompileItems>
     <LangVersion>latest</LangVersion>
@@ -14,6 +14,7 @@
   </PropertyGroup>
 
   <Import Project="..\..\build\Base.props" />
+  <Import Project="..\..\build\ReferenceAssemblies.props" />
   <Import Project="..\..\build\Rx.props" />
   <Import Project="..\..\build\ReactiveUI.props" />
   <Import Project="..\..\build\Avalonia.props" />