In Photoshop - Action and Batchor Image Processor is what you need:

http://graphicssoft.about.com/od/digitalphotography/l/blps_batch.htm

So this is how it would basically go:

1. Make Action where you create a new layer at the bottom and fill it with color.
2. Use File > Automate > Batch or File > Scripts > Image Processor to execute that recorded Action to all of the images.

Edit:

My bad!

I got thinking about it and you can also run Actions through File > Scripts > Image Processor as well. But, I'll keep that part about saving image inside Action because that allows you to save it in more formats than Image Processor

So instead of Batch use Image Processor.

Saving image in another format in Batch

Unless cs 5 has way to do this better.. Converting the file format can't be done with batch.

You can however do this:

• As part of the Action where you create new layer and fill it with color, also save the file with the format you want and to the folder you want, then close the document ctrl+w and then go to batch and select destination as none and run the Batch.

In Photoshop - Action and Batchor Image Processor is what you need:

http://graphicssoft.about.com/od/digitalphotography/l/blps_batch.htm

So this is how it would basically go:

1. Make Action where you create a new layer at the bottom and fill it with color.
2. Use File > Automate > Batch or File > Scripts > Image Processor to execute that recorded Action to all of the images.

Edit:

My bad!

I got thinking about it and you can also run Actions through File > Scripts > Image Processor as well and as you can convert the file.. if I remember correctly: jpeg, psd and tiff So, it would work better in your case.

So instead of Batch use Image Processor. 

But, I'll keep that part about saving image inside Action because that allows you to save it in more formats than Image Processor

Saving image in another format in Batch

Unless cs 5 has way to do this better.. Converting the file format can't be done with batch.

You can however do this:

• As part of the Action where you create new layer and fill it with color, also save the file with the format you want and to the folder you want, then close the document ctrl+w and then go to batch and select destination as none and run the Batch.

In Photoshop - Action and Batch is what you need:

http://graphicssoft.about.com/od/digitalphotography/l/blps_batch.htm

So this is how it would basically go:

1. Make Action where you create a new layer at the bottom and fill it with color.
2. Use Batch to execute that recorded Action to all of the images.

Unless cs 5 has way to do this better.. Converting the file format cant be done with batch.

You can however do this:

• As part of the Action where you create new layer and fill it with color, also save the file with the format you want and to the folder you want, then close the document ctrl+w and then go to batch and select destination as none and run the Batch.

or

• Run the normal action ( that doesnt have its own file saving ) in Batch and after that finishes run Files > Scripts > Image processor

In Photoshop - Action and Batchor Image Processor is what you need:

http://graphicssoft.about.com/od/digitalphotography/l/blps_batch.htm

So this is how it would basically go:

1. Make Action where you create a new layer at the bottom and fill it with color.
2. Use File > Automate > Batch or File > Scripts > Image Processor to execute that recorded Action to all of the images.

Edit:

My bad!

I got thinking about it and you can also run Actions through File > Scripts > Image Processor as well. But, I'll keep that part about saving image inside Action because that allows you to save it in more formats than Image Processor

So instead of Batch use Image Processor.

Saving image in another format in Batch

Unless cs 5 has way to do this better.. Converting the file format can't be done with batch.

You can however do this:

• As part of the Action where you create new layer and fill it with color, also save the file with the format you want and to the folder you want, then close the document ctrl+w and then go to batch and select destination as none and run the Batch.