How to access or share resource dictionary between MAUI application and library

Do you want to use the defined Colors in the Colors.xaml of MAUI project to your controls in the MAUI class library?

You defined Colors like following code in the App.xaml, right?

<Application.Resources>
    <ResourceDictionary>
        <Color x:Key="White2">#FFFFFF</Color>
        <ResourceDictionary.MergedDictionaries>        
            <ResourceDictionary Source="Resources/Styles/Colors.xaml" />
            <ResourceDictionary Source="Resources/Styles/Styles.xaml" />
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>

Will you use the ContentPage (in library) in the MAUI project? For example, if you create a ContentView that contains a Label in MAUI library.

<?xml version="1.0" encoding="utf-8" ?>
<ContentView xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MauiResourcesLibrary.NewContent1">
    <VerticalStackLayout>
        <Label
            Text="test 12312456"
             BackgroundColor="{StaticResource White2}"
            VerticalOptions="Center"
            HorizontalOptions="Center" />
    </VerticalStackLayout>
</ContentView>

In the end, you use this contentview in the MAUI project.

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:exlib="clr-namespace:MauiResourcesLibrary;assembly=MauiResourcesLibrary"
             ..>
   <ScrollView>
        <VerticalStackLayout>
            <exlib:NewContent1></exlib:NewContent1>
...

In my side, I add the MAUI project in the MAUI class library(Right click the Solution->Add->Existing Project, then I right click the MAUI project-> add-> Project Reference-> enable your MAUI class library). I right-click the MAUI project, choose the Set as Startup project. It is working in my side.