First, I'm happy to see anyone that attempts to make a windowblind. You are all welcome.
However to say you want constructive criticism while just showing a frame is like how do you like my shoes without showing everything you are wearing. Start with the startmenu and build off of that.
Take a look at some uploaded Windowblind screen shots. Show the startmenu, taskbar with buttons. Thing is you need to show more.
There are people here that will help and guide you along the way with questions you will have. As I see it you have two options if you want real opinions. One do as mentioned in reply one. Just do it. Two you really want input then show more of what you want thoughts on.
Not everyone is going to like all designs, colors, etc. As far as colors again, if you like them that is what counts. Asking people if they like the colors you are using will do little. Some will and some won't. So use what you like. Don't ever expect you are going to make all happy. MAKE yourself happy first and enjoy making a skin and uploading it here for the people to enjoy. Let the rest take it course.