How can I match Visual Studio's theme when creating a VSIX tool window?

How can I match Visual Studio's theme when creating a VSIX tool window?

You can try to binding to static VS resources:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:vs_shell="clr-namespace:Microsoft.VisualStudio.PlatformUI;assembly=Microsoft.VisualStudio.Shell.11.0">
<Style TargetType="Label">
    <Setter Property="Foreground" Value="{DynamicResource {x:Static vs_shell:EnvironmentColors.ToolWindowTextBrushKey}}"/>
</Style>
<Style TargetType="TextBox">
    <Setter Property="Foreground" Value="{DynamicResource {x:Static vs_shell:EnvironmentColors.ToolWindowTextBrushKey}}"/>
    <Setter Property="Background" Value="{DynamicResource {x:Static vs_shell:EnvironmentColors.ToolWindowBackgroundBrushKey}}"/>
</Style>
</ResourceDictionary>

See EnvironmentColors Class for more details.

Note: To get the exactly the same theme, you need use the exact XAML that VS uses. Thanks @GrantTheAnt.

As another follow up to this, when writing my Visual Studio extension, I really wanted to have my tool window appear as much like a Visual Studio window as possible. At times, I found it incredibly difficult to find the correct EnvironmentColors value. At a minimum, the correct color value should work across the default/provided Visual Studio themes. So, frustrated, I wrote a little application to help me figure out the right value, which I’ve made available at http://niahtextfilter.com/environmentcolorsfinder/. To use it, you specify the RGB color value that you want, and the application will display the most likely EnvironmentColors candidates. To get the most accurate candidates, you can provide the color you want to display per theme (dark, regular, blue) - this is easy to achieve if you take a screenshot of a sample Visual Studio UI element in each theme, and color drop the pixel you need.

It helped me match my tool window to Visual Studio reasonably well:

I hope it helps others too!

I feel as though the correct answer to this question is: you're not supposed to / Microsoft doesn't want you to do this. This post outlines the rationale behind this. The TLDR of the post seems to be that MS doesn't want third party windows looking like official VS windows, because it may cause confusion for users. I guess that's fair enough, but the flipside to that is that VS winds up looking pretty ugly with differently themed/styled windows.

If - like me - you still want to push on and style your windows like VS, the best option seems to be to go with @Leo's post above and use EnvironmentColors. You won't get the styles but you can get pretty close with the colors at least. This is a good blog which outlines some more depth on this.

I'll accept Leo's answer on the basis that it's the best solution available.