How to change signout screen color and logon screen background

Hello,

Thank you for your interest in Windows 10.

I would suggest you to follow the methods given below and check.

Follow the steps to Change the Color of the Sign In Screen in Windows.

1. Press the Win + R keyboard combination to open a run box, then type regedit and hit enter.
2. When the registry editor opens, drill down into:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Accent
3.  In the right pane of Accent, right click or press and hold on an empty area, click/tap on New and DWORD (32-bit) Value, type DefaultColorSet, and press Enter.
4. In the right pane of Accent, double click/tap on DefaultColorSet to modify it.
5. Dot Decimal, and enter a number between 0 to 24 for the color in the tables below that you want the default sign in screen to have, and click/tap on OK.

Important: This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

How to back up and restore the registry in Windows

Follow the steps to change the logon screen background

1. Press start and Click on Settings
2. Select Personalization and then click on Lock screen.
3. Select Background.

Hope this information is helpful. Please do let us know if you need further assistance with Windows, we’ll be glad to assist you.

Reference: Here is the color chart for the above post.