RadFormDecorator with RenderMode="Classic" and Silk skin renders the backgrounds of the decorated textboxes/textarea elements in gray. The issue can be seen on http://demos.telerik.com/aspnet-ajax/formdecorator/examples/rendermodes/defaultcs.aspx?skin=Silk.

Workaround: To solve the issue, switch to Lightweight RenderMode or overwrite the gray background with the following CSS class:

    <style>
        .RadForm.RadForm_Silk.rfdTextbox input[type="text"].rfdDecorated, .RadForm.RadForm_Silk.rfdTextbox input[type="password"].rfdDecorated, .RadForm.RadForm_Silk.rfdTextbox input[type="search"].rfdDecorated, .RadForm.RadForm_Silk.rfdTextbox input[type="url"].rfdDecorated, .RadForm.RadForm_Silk.rfdTextbox input[type="tel"].rfdDecorated, .RadForm.RadForm_Silk.rfdTextbox input[type="email"].rfdDecorated, .RadForm.RadForm_Silk.rfdTextarea textarea, .RadForm.RadForm_Silk.rfdTextarea textarea[disabled].rfdDecorated:hover, .RadForm.RadForm_Silk.rfdTextbox input[disabled][type="text"].rfdDecorated:hover, .RadForm.RadForm_Silk.rfdTextbox input[disabled][type="password"].rfdDecorated:hover, .RadForm.RadForm_Silk.rfdTextbox input[disabled][type="search"].rfdDecorated:hover, .RadForm.RadForm_Silk.rfdTextbox input[disabled][type="url"].rfdDecorated:hover, .RadForm.RadForm_Silk.rfdTextbox input[disabled][type="tel"].rfdDecorated:hover, .RadForm.RadForm_Silk.rfdTextbox input[disabled][type="email"].rfdDecorated:hover {
            background-color: white !important;
        }
    </style>