Color custom editor window ?

Is there a way to color custom editor window, instead of default light-grey (not input fields), thanks!

You could try this:

GUI.color = whatever; 
GUI.DrawTexture( yourrect, EditorGUIUtility.whiteTexture );

I’m not 100% sure if that is what you wish, but you can simply draw a texture before all other GUI elements, like in code below (partially copied from one of your earlier questions):

public class ScriptClassName : EditorWindow
    private static Texture2D tex;

    private static void showManipulator()
        EditorWindow.GetWindow<ScriptClassName>(false, "Something1");

        tex = new Texture2D(1, 1, TextureFormat.RGBA32, false);
        tex.SetPixel(0, 0, new Color(0.25f, 0.4f, 0.25f));

    void OnGUI()
        GUI.DrawTexture(new Rect(0, 0, maxSize.x, maxSize.y), tex, ScaleMode.StretchToFill);
        GUI.Label(new Rect(200, 200, 100, 100), "A label");
        GUI.TextField(new Rect(20, 20, 70, 30), "");