Backdrop color?

Which background color is the best for photoshop. Basically to select it and replace it with another image. In case I am unclear, like the special effects green or like the weather man.

Depends on the subject you're shooting.

A solid background color is good (like a white bed sheet evenly lit), if you're going to replace it.

Most likely portraits of my kids. I just wanted to play around with backgrounds. Is there a specific reason of the Green/Blue background? Is that easier to select?

You're better off using a white background because green/blue screens tend to bleed unless they are properly lit. If you have adequate lighting (strobes, etc) so you can light the blue/green screen to separate it from the subject then you'll be fine but other use a white backdrop.

There's nothing cheaper than a white sheet!
Browsing around, I found this which is essentially what I want to do. In the middle are examples.

Does anyone know if there is a site that provides free digital backdrops?

the green/blue screen backdrops are mostly for video production because it provides a completely separate color(s) for video mixing hardware to take and remove almost instantly, in a high quality image however, you want a backdrop of white or black, depending on the color of your background you plan to add because the green and blue will kinda blend in with the hair of the subject, or other soft edges

For keying of the background make sure you choose a color that is not going to interfere with colors in your subject and make sure to light the background evenly so that shadows from your subject, etc., do not mask or interfere with the separation between subject and background.

If you plan on adding/blending digital backgrounds into the photo, I've seen gray recommended due to the ease of blending the shadows into the new background.

My personal question is, gray muslin, velour, or paper? I would like something that can be rolled up and reused as needed, and the velour sounds great but I worry about the texture of the velour showing up. I suppose if I use f/2.0 or wider it should blur it out.

David