我没有所有图标的参考.但是，我相信黄色三角形表示存在与引用程序集相关的警告.

I don't have a reference for all the icons. However, I believe the yellow triangle indicates that there are warnings associated with referenced assembly.

通过转到错误列表(通常在 Visual Studio 底部或菜单 VIEW - Error List 或按 Ctrl + W、E)查看警告.

View the warnings by going to Error List (usually in the at the bottom of Visual Studio or in the menu VIEW - Error List or by Ctrl + W, E).

然后单击警告"选项卡.应该有一个或多个关于程序集的警告.通常存在缺失或冲突的引用或诸如无法解析主要引用 X，因为它间接依赖于具有不同版本框架的 Y.

Then click on the Warnings tab. There should be one or more warnings about the assembly. Usually there are missing or conflicting references or something like "the primary reference X could not be resolved because it has an indirect dependency on Y which has a different version of the framework.

如果您引用为 .NET 框架的新版本构建的程序集，则可能会发生这种情况.(例如，您的程序集使用 .NET 4.0，但您要使用的程序集是使用 .NET 4.5 构建的).

This could happen if you reference an assembly that is built for a new version of the .NET framework. (Example your assembly is using .NET 4.0 but the assembly you want to use is built with .NET 4.5).