Here is a guide for creating a gray colored fade in Windows Movie Maker.
The most common transition, yet found in the video effects area in Windows Movie Maker, is the Fade Out. Conventionally this is a Fade Out to Black or a Fade In From Black, which is what you get when you choose one of the fades from the right click menu. Occasionally you can get a Fade Out to White or Fade In to White, which is a polarized option that is much more intense. In other non-linear video editing software there can be a whole host of other colors, yet these are the only two that are built in to Windows Movie Maker. There is one other option that is available in Windows Movie Maker and it is Fade Out to Variable Shades of Gray.
To achieve a gray color fade on your video clip you have to stack to other effects. Right click your video clip and bring up the Video Effects menu. Decide whether you are looking to Fade In or Fade Out and find the options. You are going to have one for each: black and white. Go ahead and select one of each, hit Add in the middle, and once it is in the right hand column hit OK. You will now see that your Windows Movie Maker video clip now has a Fade In From Gray or Fade Out to Gray right there.
Shades of Gray
You can even shift the shade of gray easily. This is done by compounding either the black or white fades. If you want a darker shade of gray then you can add several more of the black fade. If you want to lighten it up a little bit you add more of the white fades. You can only have a total of six video effects on any given video clip in Windows Movie Maker so there is an over all limit to how much you can actually control the color scheme.
One thing you do have to watch out for is that when you stack video effects, especially the same one, it may cause some slow down. This is especially true with the fades as it is really the same action happening several times over.